Check for upper bounds of nselectors.

Currently there is no check for the upper bounds of the
nselectors. Hence, a corrupt input can cause a segfault.

This issue was discovered by one of our fuzzers. The actual error was:

../bzip2-1.0.6/decompress.c:299:10: runtime error: index 18002 out of bounds for type 'UChar [18002]'

Change-Id: I1f749ca7a54cce95d671f184b6425ac659767ffc
1 file changed