group move probably caused segfault

Was not able to reproduce it, but I think the group move command caused the following segmentation fault (I have a core dump as well):

# Backtrace

#0 0x00007f9c9f996d7f in raise () at /usr/lib/libc.so.6
#1 0x00007f9c9f981672 in abort () at /usr/lib/libc.so.6
#2 0x00007f9c9f981548 in _nl_load_domain.cold.0 () at /usr/lib/libc.so.6
#3 0x00007f9c9f98f396 in () at /usr/lib/libc.so.6
#4 0x00007f9c89608006 in COMMIT::makeEntry(EDA_ITEM*, CHANGE_TYPE, EDA_ITEM*) (this=0x5630174e6d20, aItem=0x563016fe0610, aType=CHT_MODIFY, aCopy=0x0)
    at /home/thomas/Projekte/Kicad/kicad-source-mirror/common/commit.cpp:158
#5 0x00007f9c89607b5e in COMMIT::createModified(EDA_ITEM*, EDA_ITEM*, int) (this=0x5630174e6d20, aItem=0x563016fe0610, aCopy=0x0, aExtraFlags=0)
    at /home/thomas/Projekte/Kicad/kicad-source-mirror/common/commit.cpp:149
#6 0x00007f9c89607a17 in COMMIT::Stage(EDA_ITEM*, CHANGE_TYPE) (this=0x5630174e6d20, aItem=0x563016fe0610, aChangeType=CHT_MODIFY) at /home/thomas/Projekte/Kicad/kicad-source-mirror/common/commit.cpp:67
#7 0x00007f9c889da112 in COMMIT::Modify(EDA_ITEM*) (this=0x5630174e6d20, aItem=0x563016fe0610) at /home/thomas/Projekte/Kicad/kicad-source-mirror/include/commit.h:105
#8 0x00007f9c88e19db8 in EDIT_TOOL::Main(TOOL_EVENT const&) (this=0x563016dcba90, aEvent=...) at /home/thomas/Projekte/Kicad/kicad-source-mirror/pcbnew/tools/edit_tool.cpp:456
#9 0x00007f9c88e29879 in std::__invoke_impl<int, int (EDIT_TOOL::*&)(TOOL_EVENT const&), EDIT_TOOL*&, TOOL_EVENT const&>(std::__invoke_memfun_deref, int (EDIT_TOOL::*&)(TOOL_EVENT const&), EDIT_TOOL*&, TOOL_EVENT const&) (__f=@0x563016846290: (int (EDIT_TOOL::*)(EDIT_TOOL * const, const TOOL_EVENT &)) 0x7f9c88e18fe0 <EDIT_TOOL::Main(TOOL_EVENT const&)>, __t=@0x5630168462a0: 0x563016dcba90, __args=...)
    at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/bits/invoke.h:73
#10 0x00007f9c88e29777 in std::__invoke<int (EDIT_TOOL::*&)(TOOL_EVENT const&), EDIT_TOOL*&, TOOL_EVENT const&>(int (EDIT_TOOL::*&)(TOOL_EVENT const&), EDIT_TOOL*&, TOOL_EVENT const&) (__fn=
    @0x563016846290: (int (EDIT_TOOL::*)(EDIT_TOOL * const, const TOOL_EVENT &)) 0x7f9c88e18fe0 <EDIT_TOOL::Main(TOOL_EVENT const&)>, __args=@0x5630168462a0: 0x563016dcba90, __args=...)
    at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/bits/invoke.h:95
#11 0x00007f9c88e29705 in std::_Bind<int (EDIT_TOOL::*(EDIT_TOOL*, std::_Placeholder<1>))(TOOL_EVENT const&)>::__call<int, TOOL_EVENT const&, 0ul, 1ul>(std::tuple<TOOL_EVENT const&>&&, std::_Index_tuple<0ul, 1ul>) (this=0x563016846290, __args=...) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/functional:400
#12 0x00007f9c88e29641 in std::_Bind<int (EDIT_TOOL::*(EDIT_TOOL*, std::_Placeholder<1>))(TOOL_EVENT const&)>::operator()<TOOL_EVENT const&, int>(TOOL_EVENT const&) (this=0x563016846290, __args=...)
    at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/functional:482
#13 0x00007f9c88e292f2 in std::_Function_handler<int (TOOL_EVENT const&), std::_Bind<int (EDIT_TOOL::*(EDIT_TOOL*, std::_Placeholder<1>))(TOOL_EVENT const&)> >::_M_invoke(std::_Any_data const&, TOOL_EVENT const&) (__functor=..., __args=...) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/bits/std_function.h:282
#14 0x00007f9c896fc068 in std::function<int (TOOL_EVENT const&)>::operator()(TOOL_EVENT const&) const (this=0x5630172a1ac8, __args=...)
    at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/8.2.1/../../../../include/c++/8.2.1/bits/std_function.h:687
#15 0x00007f9c896fbe9d in COROUTINE<int, TOOL_EVENT const&>::callerStub(long) (aData=140724165634392) at /home/thomas/Projekte/Kicad/kicad-source-mirror/include/tool/coroutine.h:331
#16 0x00007f9c89766671 in make_fcontext () at /usr/bin/_pcbnew.kiface
#17 0x0000000000000000 in ()

# Version Information

Application: kicad
Version: (5.1.0-rc1-66-gec59361f7), debug build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.63.0 OpenSSL/1.1.1a zlib/1.2.11 libidn2/2.1.0 libpsl/0.20.2 (+libidn2/2.1.0) libssh2/1.8.0 nghttp2/1.35.1
Platform: Linux 4.20.6-arch1-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.69.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.63.0
    Compiler: Clang 7.0.1 with C++ ABI 1002

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON