readelf: Calculate max_entries instead of needed bytes (and overflowing).

readelf: Calculate max_entries instead of needed bytes (and overflowing).

The afl fuzzer found that we would overflow the needed bytes when
calculating how many index entries would fit in the .debug_loclists
and .debug_rnglists tables. To fix this just calculate the max number
of entries. If the offset entry count is larger than that, do emit
an error, but print up to max_entries of offsets (so the user can
more clearly see what is wrong with their table).

Signed-off-by: Mark Wielaard <mark@klomp.org>