HOPKINS: Add null termination to byte buffer returned by loadFile().

This shouldn't be a problem, as current client code either must find a
terminator when parsing the byte buffer or have preknowledge of the
buffer size from a file size or fixed call, so the appended null
termination will not cause issues. This change thus allows client code
to add sanity checks to prevent reading off the end of the buffer.
HOPKINS: Add sanity check to parsing of COMPUTAN.TXT file.

This previously crashed on the Polish version due to a variant file
format causing the parsing to make several invalid memory accesses.

This prevents this crash and any other in future, though it does not
fix the parsing of the variant file format.