fix for the 32-bit fix

Sorry for the noise,
I've just realized that my last patch is not enough.
Compression can enlarge the result, therefore the result of LZ4_compressBound is larger and can wrap, e.g. LZ4.compress_bound max_int is a negative number. Here's a better fix.
Or introduce another exception for this case? It at least doesn't fail for the reason mentioned in the interface file.