Code review comment for lp:~widelands-dev/widelands/bug-1653460-panel-init-width

Crash when accessing "About Widelands":

This is Widelands Version bzr8310[bug-1653460-panel-init-width] (Debug)
[...]
widelands: /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/panel.cc:243: void UI::Panel::set_size(int, int): Assertion `nw >= 0' failed.

Thread 1 "widelands" received signal SIGABRT, Aborted.
0x00007ffff513b04f in raise () from /usr/lib/libc.so.6
(gdb) backtrace
#0 0x00007ffff513b04f in raise () from /usr/lib/libc.so.6
#1 0x00007ffff513c47a in abort () from /usr/lib/libc.so.6
#2 0x00007ffff5133ea7 in __assert_fail_base () from /usr/lib/libc.so.6
#3 0x00007ffff5133f52 in __assert_fail () from /usr/lib/libc.so.6
#4 0x0000000000edafe4 in UI::Panel::set_size (this=0x1d47c20, nw=-10, nh=-49)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/panel.cc:243
#5 0x0000000000ecb775 in UI::FileViewPanel::update_tab_size (this=0x7fffffffce00, index=0)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/fileview_panel.cc:68
#6 0x0000000000ecb8c6 in UI::FileViewPanel::layout (this=0x7fffffffce00)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/fileview_panel.cc:83
#7 0x0000000000ef656b in UI::TabPanel::update_desired_size (this=0x7fffffffce00)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/tabpanel.cc:158
#8 0x0000000000ef6971 in UI::TabPanel::add_tab (this=0x7fffffffce00, width=74, name="about_0", title="Readme", pic=0x21ed330, tooltip_text="", panel=0x1d59920)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/tabpanel.cc:207
#9 0x0000000000ef6660 in UI::TabPanel::add (this=0x7fffffffce00, name="about_0", title="Readme", panel=0x1d59920, tooltip_text="")
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/tabpanel.cc:170
#10 0x0000000000ecb41f in UI::FileViewPanel::add_tab (this=0x7fffffffce00, lua_script="txts/README.lua")
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_basic/fileview_panel.cc:59
#11 0x0000000000f019e8 in FullscreenMenuAbout::FullscreenMenuAbout (this=0x7fffffffca80)
    at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/ui_fsmenu/about.cc:39
#12 0x0000000000c3138f in WLApplication::mainmenu (this=0x1960b10) at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/wlapplication.cc:1017
#13 0x0000000000c2de4c in WLApplication::run (this=0x1960b10) at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/wlapplication.cc:444
#14 0x0000000000c2c4c1 in main (argc=1, argv=0x7fffffffe5b8) at /home/kaputtnik/Quellcode/widelands-repo/bug-1653460-panel-init-width/src/main.cc:49