another fix for huge data (Re: a compression tool useful with constrained memory)

Noticed a situation where we would divide by zero:

+ * version 0.2015-04-29
+ *         avoid division by zero when the input length
+ *         differs from N*4GB less than 100 bytes

Attaching a patch which should apply cleanly (build tested with
a different patch version, for the original source format).

Regards,
Rl