Playing CLUT8 videos (such as FLIC videos) was not working properly:

• If the game itself is CLUT8, it was using the previously set palette from the game and ignore the one from the video decoder, resulting in wrong colors.
• If the game uses 16bit or 32bit colors, it was crashing as the decoder palette was not passed to the blitting code that was expected it.

There were two separate crash:

• If the video is stretched in AGS, it was asserting in Graphics::transBlitPixel due to the source palette being a nullptr pointer.
• If the video is not stretched in AGS, it was trying to access 0x0 memory. There was an incorrect assert that was not triggered and should have caught this before getting to the invalid memory access.

The ManagedSurface blitting code only allowed blitting from CLUT8 source to non-CLUT8 destination if the source was itself a ManagedSurface. This pull request adds the possibility to do this also if the source is a Surface (such as a VideoDecoder frame). This is used in the AGS engine to fix the crash mentioned above.

Crash call-stack for the CLUT8 -> 16/32bit color (for stretched videos, the non-stretch one is similar but crashes in ManagedSurface::blitFromInner instead):

Assertion failure: 'srcPalette != nullptr' in graphics/managed_surface.cpp:558 (void Graphics::transBlitPixel(TSRC, TDEST &, const Graphics::PixelFormat &, const Graphics::PixelFormat &, uint32, uint32, const uint32 *, const byte *) [TSRC = unsigned char, TDEST = unsigned int])
  #04  __assert2 40)
  #05  void Graphics::transBlitPixel<unsigned char, unsigned int>(unsigned char, unsigned int&, Graphics::PixelFormat const&, Graphics::PixelFormat const&, unsigned int, unsigned int, unsigned int const*, unsigned char const*) 548)
  #06  void Graphics::transBlit<unsigned char, unsigned int>(Graphics::Surface const&, Common::Rect const&, Graphics::ManagedSurface&, Common::Rect const&, unsigned char, bool, unsigned int, unsigned int, unsigned int const*, unsigned int const*, Graphics::Surface const*, bool) 1048)
  #07  Graphics::ManagedSurface::transBlitFromInner(Graphics::Surface const&, Common::Rect const&, Common::Rect const&, unsigned int, bool, unsigned int, unsigned int, unsigned int const*, unsigned int const*, Graphics::Surface const*, bool) 460)
  #08  Graphics::ManagedSurface::transBlitFrom(Graphics::Surface const&, Common::Rect const&, Common::Rect const&, unsigned int, bool, unsigned int, unsigned int, Graphics::Surface const*, bool) 36)
  #09  AGS3::play_video(Video::VideoDecoder*, char const*, int, AGS3::VideoSkipType, bool) 524)
  #10  AGS3::play_flc_video(int, int, AGS3::VideoSkipType) 72)

Example of wrong color for CLUT8 -> CLUT8:
Before

After

I am opening this pull request to check there is no compilation error before committing (I only compiled with the AGS engine locally) and give the opportunity to those who want to review the changes to the Graphics::ManagedSurface code. I think it is straightforward, but I may have overlooked something.