plMipmap::CompressImage Buffer Overrun

[Hoikas]

plMipmap::CompressImage (squish) appears to overrun the image data buffer when compressing a DXT5 mip level of 1x1. In most cases, this does not appear to crash on Windows x64. However, I have observed a few scenarios where the MSVCRT detects this overrun on deleting the image data, crashing the application. Specifically, using a 160x160 JPEG that was resized to 128x128 in Blender (the image buffer I provide is RGBA). This behavior can be debugged by using the Windows Debug Toolkit's gflags.exe /p /enable <appname.exe>.

AFAICT our level size calculation is only allocating enough buffer for the alpha block in, so when squish tries to write the color block, it corrupts the heap.

A potentially related issue: when exporting a DDS from PRPShop and attempting to import the same DDS yields a read-past-eof error. PRPShop consistently requests 12 more bytes than is available in the stream.