Fix quadratic loops in pentaxmn_int.cpp

[kevinbackhouse]

Fixes: #1909

I didn't add a test because the poc attached to #1909 is quite big. (You need a large file for the quadratic loop to take a noticeable amount of time to run.)

The fix is to search from the current position, rather than repeatedly searching from the beginning of the string.

[codecov]

Codecov Report

Merging #1910 (dfcc305) into main (774e662) will increase coverage by 0.00%.
The diff coverage is 50.00%.

❗ Current head dfcc305 differs from pull request most recent head 9f1e3e3. Consider uploading reports for the commit 9f1e3e3 to get more accurate results

@@           Coverage Diff           @@
##             main    #1910   +/-   ##
=======================================
  Coverage   60.87%   60.87%           
=======================================
  Files          96       96           
  Lines       19041    19043    +2     
  Branches     9726     9726           
=======================================
+ Hits        11591    11593    +2     
  Misses       5138     5138           
  Partials     2312     2312           

Impacted Files	Coverage Δ
src/pentaxmn_int.cpp	72.92% <50.00%> (+0.23%)	⬆️

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[kmilos]

LGTM

[kevinbackhouse]

@Mergifyio backport 0.27-maintenance

[mergify]

Command backport 0.27-maintenance: success

Backports have been created

• #1924 Fix quadratic loops in pentaxmn_int.cpp (backport #1910) has been created for branch 0.27-maintenance