Fix getCommandOption for command-only packets

[s-genereux]

Pcap++ crashes when you attempt to getCommandOption() of a command-only FTP request packet. I traced the issue to SingleCommandTextProtocol::getCommandOptionInternal().

To check for command-only packets, it compares the offset to the option field returned by getArgumentFieldOffset() to the raw data length minus 1. This should be minus 2;

1. -1 to account for the fact getArgumentFieldOffset() returns the position of the CR in the CRLF terminator in the case of command-only packets.
2. -1 to account for the fact we are comparing a length value to a zero-indexed position value.

This PR makes the necessary change in SingleCommandTextProtocol.cpp and adds a command-only FTP request packet testcase to Packet++Test

[egecetin]

Fails due to brownouts. Need to run CI later

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.12%. Comparing base (3292f14) to head (b88e964).

Additional details and impacted files

@@           Coverage Diff            @@
##              dev    #1718    +/-   ##
========================================
  Coverage   83.11%   83.12%            
========================================
  Files         279      279            
  Lines       48399    48408     +9     
  Branches    10237    10617   +380     
========================================
+ Hits        40227    40238    +11     
- Misses       7035     7439   +404     
+ Partials     1137      731   -406     

Flag	Coverage Δ
alpine320	75.09% <100.00%> (+0.01%)	⬆️
fedora40	75.15% <100.00%> (+0.04%)	⬆️
macos-13	80.61% <100.00%> (+0.01%)	⬆️
macos-14	80.61% <100.00%> (+0.01%)	⬆️
macos-15	80.58% <100.00%> (+0.01%)	⬆️
mingw32	70.85% <100.00%> (+0.01%)	⬆️
mingw64	70.80% <100.00%> (-0.01%)	⬇️
npcap	85.23% <100.00%> (ø)
rhel94	74.97% <100.00%> (+0.02%)	⬆️
ubuntu2004	58.59% <30.00%> (+<0.01%)	⬆️
ubuntu2004-zstd	58.71% <30.00%> (+<0.01%)	⬆️
ubuntu2204	74.91% <100.00%> (+0.03%)	⬆️
ubuntu2204-icpx	61.29% <100.00%> (+0.01%)	⬆️
ubuntu2404	75.13% <100.00%> (+0.02%)	⬆️
unittest	83.12% <100.00%> (+<0.01%)	⬆️
windows-2019	85.26% <100.00%> (+<0.01%)	⬆️
windows-2022	85.28% <100.00%> (+<0.01%)	⬆️
winpcap	85.25% <100.00%> (+0.01%)	⬆️
xdp	50.42% <100.00%> (+0.02%)	⬆️

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