decompress_generic: re-add fastpath
decompress_generic: re-add fastpath

This is the remaineder of the original 'shortcut'.  If true, we can avoid
the loop in LZ4_wildCopy, and directly copy instead.

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso