pcbnew VRML export dialog settings have no effect

The pcbnew VRML export dialog settings are not honored at least with bzr revno 6403.

Steps to reproduce:
- Load a board design
- Go to File->Export->VRML
- Try changing export settings from the defaults (in particular "Plain PCB (no copper or silk)", "Copy 3D model files..", "Use relative paths..", or Output Units).
- Click OK button to export to the VRML file.
- Note that changed settings did not take effect in exported VRML file (initial dialog settings are used).

Problem is in PCB_EDIT_FRAME::OnExportVRML function in pcbnew/dialogs/dialog_export_vrml.cpp. The dialog settings are read prior to creating the dialog with ShowModal() when they should be read after returning from ShowModal().

Patch attached which fixes this issue.

Additional version information:
Application: pcbnew
Version: (2015-12-22 BZR 6403)-product debug build
wxWidgets: Version 3.0.2 (debug,wchar_t,compiler with C++ ABI 1009,GCC 5.2.1,wx containers,compatible with 2.8)
Platform: Linux 4.2.0-22-generic x86_64, 64 bit, Little endian, wxGTK
Boost version: 1.58.0
libcurl version: 7.43.0 (with SSL - OpenSSL/1.0.2d)
         USE_WX_GRAPHICS_CONTEXT=OFF
         USE_WX_OVERLAY=OFF
         KICAD_SCRIPTING=OFF
         KICAD_SCRIPTING_MODULES=OFF
         KICAD_SCRIPTING_WXPYTHON=OFF
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=OFF