SDL2/WIN10: Segfault after locking/unlocking the computer

[rootfather]

Note: This issue was first discovered by waltervn.

When building the latest ScummVM codebase with SDL2 and the msys2/mingw-w64 toolchain, ScummVM crashes with a segmentation fault after locking/unlocking the computer either due to inactivity or manually by pressing Win+L.

After unlocking, ScummVM crashes instantly in fullscreen mode. In windowed mode, ScummVM crashes as soon as the cursor is moved inside the ScummVM window. The crash occures when displaying the launcher as well as while an game engine is running.

My setup:
ScummVM revision 03cf470
SDL 2.0.4
GCC 6.1.0 from the msys2 toolchain
Windows 10, Insider Build 14905 [other builds might be affected too]
AMD integrated graphics

The crash occures with the SDL2.dll binary shipped with msys2 as well as the one inside the scummvm_libs2015 package and even the official one from libsdl.org (all .dlls are version 2.0.4).

Thankfully, the SDL2.dll from the ScummVM Libs package has debug symbols in it, so here's the backtrace right after unlocking the computer (and crashing ScummVM).

Starting program: C:\users\user\git\scummvm\scummvm.exe
[New Thread 22604.0x4564]
[New Thread 22604.0x4f74]
[New Thread 22604.0x55dc]
[New Thread 22604.0x42cc]
[New Thread 22604.0x1ca0]
[New Thread 22604.0x5b78]
[New Thread 22604.0x5fd0]
[New Thread 22604.0x5b34]
[New Thread 22604.0x5cc4]
[New Thread 22604.0x5d38]
[New Thread 22604.0x36c0]
[New Thread 22604.0x5cf4]
[New Thread 22604.0x5cac]
[New Thread 22604.0x441c]
[New Thread 22604.0x46e8]

Thread 1 received signal SIGSEGV, Segmentation fault.
0x00007ffac14f9bfd in SDL_UnlockSurface () from C:\msys64\mingw64\bin\SDL2.dll
(gdb) backtrace
#0  0x00007ffac14f9bfd in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#1  0x00007ffac14f5a31 in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#2  0x00007ffac14f94d7 in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#3  0x00007ffac14f89e8 in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#4  0x00007ffac14f1370 in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#5  0x00007ffac14b7184 in SDL_UnlockSurface ()
   from C:\msys64\mingw64\bin\SDL2.dll
#6  0x000000000046704d in SurfaceSdlGraphicsManager::SDL_UpdateRects (
    this=0x37ed070, screen=0x3778430, numrects=1, rects=0x37ed1dc)
    at backends/graphics/surfacesdl/surfacesdl-graphics.cpp:2491
#7  0x00000000004632aa in SurfaceSdlGraphicsManager::internUpdateScreen (
    this=0x37ed070)
    at backends/graphics/surfacesdl/surfacesdl-graphics.cpp:1261
#8  0x0000000000462572 in SurfaceSdlGraphicsManager::updateScreen (
    this=0x37ed070)
    at backends/graphics/surfacesdl/surfacesdl-graphics.cpp:1018
#9  0x0000000000458f14 in ModularBackend::updateScreen (this=0x37d5050)
    at backends/modular-backend.cpp:149
#10 0x0000000000414b89 in GUI::GuiManager::runLoop (this=0x3832920)
    at gui/gui-manager.cpp:304
#11 0x000000000040ffc5 in GUI::Dialog::runModal (this=0x1879d70)
    at gui/dialog.cpp:80
#12 0x0000000000404ad0 in launcherDialog () at base/main.cpp:96
#13 0x00000000004066b0 in scummvm_main (argc=1, argv=0x37c2b80)
    at base/main.cpp:481
#14 0x0000000000403a1d in SDL_main (argc=1, argv=0x37c2b80)
    at backends/platform/sdl/win32/win32-main.cpp:72
#15 0x0000000000403968 in WinMain ()
    at backends/platform/sdl/win32/win32-main.cpp:55
#16 0x00000000005d5772 in main (flags=<optimized out>,
    cmdline=<optimized out>, inst=<optimized out>)
    at C:/repo/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crt0_c.c:18
#17 0x00000000004013f8 in __tmainCRTStartup ()
    at C:/repo/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crtexe.c:334
#18 0x00000000004014eb in WinMainCRTStartup ()
    at C:/repo/mingw-w64-crt-git/src/mingw-w64/mingw-w64-crt/crt/crtexe.c:184

Unfortunately, I was unable to compile the latest SDL2 code from the HG repository due to compilation errors while compiling some DirectX components.