Example of fix:

❯ src/tcprewrite -r 1:2 -i ping.pcap -c ping.cache -o out.pcap
❯ src/tcprewrite -r 1-:2 -i ping.pcap -c ping.cache -o out.pcap

Fatal Error in ../../src/tcprewrite.c:main() line 86:
 Unable to parse args: From ../../../src/tcpedit/parse_args.c:tcpedit_post_args() line 189:
Unable to parse --portmap=1-:2

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• stop and throw an error on --portmap syntax error