CODEC-311: Fix possible ArrayIndexOutOfBoundException thrown by RefinedSoundex.getMappingCode()

[arthurscchan]

This fixes a possible ArrayIndexOutOfBoundException in src/main/java/org/apache/commons/codec/language/RefinedSoundex.java thrown by RefinedSoundex.getMappingCode() method when handling out of range letters.

This PR adds a conditional checking to ensure the index is never out of bounds from the configured soundexMapping array. If the calculated index goes out of bounds, it will simply return 0, just like the original logic when Character.isLetter() returns false.

We found this bug using fuzzing by way of OSS-Fuzz. It is reported at https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=64353.

[garydgregory]

Hello @arthurscchan
You'll need a unit test to prove this change works.

[arthurscchan]

@garydgregory Thanks for the comment. I have added a unit test.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (44e4c4d) 92.27% compared to head (a9c487e) 92.22%.
Report is 8 commits behind head on master.

Files	Patch %	Lines
.../apache/commons/codec/language/RefinedSoundex.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #219      +/-   ##
============================================
- Coverage     92.27%   92.22%   -0.05%     
- Complexity     1742     1747       +5     
============================================
  Files            67       67              
  Lines          4584     4594      +10     
  Branches        709      714       +5     
============================================
+ Hits           4230     4237       +7     
- Misses          242      243       +1     
- Partials        112      114       +2     

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[garydgregory]

@arthurscchan
Please use a better description in PRs and JIRA: Specify the class and method where the exception occurs.