fix potential overflow that can lead to infinite loop in file reading

[hellkite500]

A potential overflow bug exists in the read_file_line_counts function. Depending on system, compiler, and hardware, this can lead to a infinite loop.

Changes

• Change the i/o buffer type for character reading to int from char to avoid overflowing a possible unsigned char type.

Testing

1. Tested through ngen unit tests

Checklist

• [x] PR has an informative and human-readable title
• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows project standards (link if applicable)
• [x] Passes all existing automated tests
• [x] Any change in functionality is tested
• [x] New functions are documented (with a description, list of inputs, and expected output)
• [x] Placeholder code is flagged / future todos are captured in comments
• [x] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• [x] Reviewers requested with the Reviewers tool :arrow_right:

Testing checklist

Target Environment support

• [x] Linux (x86 and arm)
• [x] MacOS (x86 and arm)