releasetools: Support verifying files with non-monotonic ranges.

Fixes: 79951650
Test: Run validate_target_files on target_files.zip with files in
      non-monotonic ranges.
Test: python -m unittest test_validate_target_files
Test: python3 -m unittest test_validate_target_files
Change-Id: I82571d3358598775de4cdeb5e64035689fea6487