[PATCH] winedbg: avoid crashing when reading pdb

[André Johansen]

I got a case where winedbg crashes when reading a pdb file, because
"root" is 0.

Unhandled exception: page fault on read access to 0x00000000 in 32-bit code (0x405a7e37).
In 32-bit mode.
0x405a7e37 (DEBUG_ProcessPDBFile+0x11f [msc.c:2590] in winedbg.exe.so): movl    0x0(%edx),%eax
2590        switch ( root->version )
Wine-dbg>cont
First chance exception: page fault on read access to 0x00000000 in 32-bit code (0x405a7e37).
Register dump:
 CS:0023 SS:002b DS:002b ES:002b FS:003b GS:0033
 EIP:405a7e37 ESP:407f29f4 EBP:407f2ac8 EFLAGS:00010246(  R- 00  I  Z- -P1 )
 EAX:407f2a3c EBX:405c44a8 ECX:00000000 EDX:00000000
 ESI:40aa5010 EDI:00000003
Stack dump:
0x407f29f4 (_end+0x212f90):  407f2a3c 407f2a30 00000000 407f2a7c
0x407f2a04 (_end+0x212fa0):  00000000 40ab0000 00000000 00000003
0x407f2a14 (_end+0x212fb0):  00000002 407f2a20 00000000 00000000
0x407f2a24 (_end+0x212fc0):  00000000 00000000 40ab0000 00000000
0x407f2a34 (_end+0x212fd0):  0000004c 00000050 00000000 00000000
0x407f2a44 (_end+0x212fe0):  00000000 00000000 00000000 00000000
0x407f2a54 (_end+0x212ff0):

Backtrace:
=>0 0x405a7e37 (DEBUG_ProcessPDBFile+0x11f(module=0x3c9a6758, filename=0x40aa5010, timestamp=0x38e8c154) [msc.c:2590] in winedbg.exe.so) (ebp=407f2ac8)
  1 0x405a81ba (DEBUG_ProcessCodeView+0x6e(module=0x3c9a6758, root=0x40aa5000) [msc.c:2833] in winedbg.exe.so) (ebp=407f2af4)
  2 0x405a837f (DEBUG_ProcessDebugDirectory+0xb7(module=0x3c9a6758, file_map=0x408f0000, dbg=0x40a0d000, nDbg=0x1) [msc.c:2874] in winedbg.exe.so) (ebp=407f2b0c)
  3 0x405a86b1 (DEBUG_RegisterMSCDebugInfo+0x239(module=0x3c9a6758, hFile=0x44, _nth=0x407f2bc0, nth_ofs=0xf8) [msc.c:3064] in winedbg.exe.so) (ebp=407f2b5c)
  4 0x405a54b5 (DEBUG_LoadModule32+0x185(name=0x407f2ce8, hFile=0x44, base=0x40892000) [module.c:307] in winedbg.exe.so) (ebp=407f2ccc)
  5 0x405afae4 (.L280+0x51 [winedbg.c] in winedbg.exe.so) (ebp=407f2df4)
  6 0x405afda2 (DEBUG_MainLoop+0x42 [winedbg.c:959] in winedbg.exe.so) (ebp=407f2e68)
  7 0x405b00c7 (main+0xbf(argc=0x2, argv=0xbfffdd18) [winedbg.c:1182] in winedbg.exe.so) (ebp=407f2e9c)
  8 0x4059916c (__wine_exe_main+0x38 [winedbg.exe.spec.c:556] in winedbg.exe.so) (ebp=407f2eb0)
  9 0x400892ae (start_process+0x22e(arg=0x0) [process.c:1622] in libntdll.dll.so) (ebp=407f2ff4)
  10 0x400a6d54 (SYSDEPS_SwitchToThreadStack+0x14 in libntdll.dll.so) (ebp=00000000)

0x405a7e37 (DEBUG_ProcessPDBFile+0x11f [msc.c:2590] in winedbg.exe.so): movl    0x0(%edx),%eax
2590        switch ( root->version )


Changes:
Avoid crashing when unable to read pdb file.

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