[Bug 41977] Gunner3 always crashes due to wine having a different allocation scheme than windows

https://bugs.winehq.org/show_bug.cgi?id=41977

--- Comment #2 from Fabian Maurer  ---
The game seems to turn an unsigned 16Bit integer into an 32Bit integer. Once
the number is too big, it gets treated as negative and gets subtracted.
The patch turns a "movsx" into a "movzx", essentially forcing unsigned mode and
fixing the crashes.

Technically, it could read up to 32768 bytes before the allocated memory, but
according to my tests a buffer of 5500 bytes is enough to avoid crashes.