opengl32: work around a crash in glGetString

[Louis. Lenders]

Hi this fixes http://bugs.winehq.org/show_bug.cgi?id=13599

A +relay trace shows glGetString is crashing inside glGetString. The cause is _not_ a lacking  opengl context setup around glGetString. I did some testing and both on windows and wine glGetString  just returns NULL if this is the case, but it never crashes inside glGetString:

/* glGetString without opengl context: */
0009:Call opengl32.glGetString(00001f01) ret=004016bc
0009:Ret  opengl32.glGetString() retval=00000000 ret=004016bc

/* Crash from Autocad */

0064:Call opengl32.glGetString(00001f01) ret=1000cd58
0064:trace:seh:raise_exception code=c0000005 flags=0 addr=0x60ec12f6
0064:trace:seh:raise_exception  info[0]=00000000
/* and never returns*/


This bug has been reproduced by several other people , so it's also not due to a bad gl-setup on my side. In case you want to try , Autocad trial 2004 can be downloaded from http://www.brothersoft.com/autocad-78351.html. It's the main issue that prevent autocad 2004 up to 2008 from running.

So for now my conclusion is, this is a nasty bug outside wine, and an exception handler is needed to work around the crash. If the patch is rejected i would appreciate some input. Thanks and regards



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