Add some additional checks in SnifferDecompress().

Check the input pointer in the while clause of the loop, so that we
handle an empty input buffer.

When reading a bit mask, check before fetching the bit mask that we have
two bytes of bit mask and the byte after it.

Before putting an uncompressed input byte into the output, make sure we
wouldn't run past the end of the output buffer.

Before copying an earlier string from the output buffer, make sure it
doesn't run past the end of the data we've decompressed so far.

Bug: 10461
Change-Id: I8bb8d0d291368ae8bf0ac26970ff54d3262a7e6e
Reviewed-on: https://code.wireshark.org/review/4083
Reviewed-by: Guy Harris <guy@alum.mit.edu>