line number for files with no newline

[kroening]

The parser sets the line number used for error messages once reaching a newline. This fixes the logic for the case that the input file does not have a newline.

This is only visible on .i files, as the preprocessor adds a newline when there isn't one on .c files.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.60%. Comparing base (e5e5c65) to head (6ee9f5b).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8558      +/-   ##
===========================================
+ Coverage    79.14%   79.60%   +0.45%     
===========================================
  Files         1733     1733              
  Lines       198512   197381    -1131     
  Branches     18173    18173              
===========================================
+ Hits        157119   157122       +3     
+ Misses       41393    40259    -1134     

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