fix: fixed two bugs in the ipc ghidra script

[jstucke]

• fixed AttributeError in get_vars_from_varnode
• fixed IndexError in filter_relevant_indices

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.01980% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.52%. Comparing base (e1011ca) to head (c4da184).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/plugins/analysis/ipc/test/test_ipc_ghidra.py	98.01%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1467      +/-   ##
==========================================
+ Coverage   92.40%   92.52%   +0.11%     
==========================================
  Files         370      371       +1     
  Lines       20829    20901      +72     
==========================================
+ Hits        19248    19338      +90     
+ Misses       1581     1563      -18     

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