Wrong number of bits skipped while decoding an empty UTF8String on UPER packet

Summary

If a PER packet contains an empty UTF8 string, the offset is skipped by 9 bits instead of 8, resulting on wrong decoding of subsequent fields.

Steps to reproduce

Dissect a packet containing an empty (null-termination char only) UTF8 string.

What is the current bug behavior?

What is the expected correct behavior?

(What you should see instead)

Sample capture file

Relevant logs and/or screenshots

On dissect_per_restricted_character_string_sorted, the string length is checked and one bit is skipped in case it is 0 to point to the next element. However, the offset is already advanced by 8 bits from the calling dissect_per_length_determinant function. On my private build, saving the offset prior to calling dissect_per_length_determinant and checking if any bits were skipped (instead of the string length) has solved the issue.

Build information

(In Wireshark, select Help->About Wireshark from the main menu and use the button "Copy To Clipboard". Please paste the complete output here. Or from the command line, run `tshark -v` or `wireshark -v`)