refactor: improving MedianOfMatrix

[alxkm]

• Added a check to throw IllegalArgumentException if the input matrix contains no elements.
• Prevents undefined behavior when computing median on empty data.
• Ensures more robust and predictable method behavior.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.63%. Comparing base (ef93cc1) to head (69bbb70).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/matrix/MedianOfMatrix.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6376      +/-   ##
============================================
- Coverage     74.64%   74.63%   -0.01%     
  Complexity     5445     5445              
============================================
  Files           682      682              
  Lines         19000    19002       +2     
  Branches       3668     3670       +2     
============================================
+ Hits          14182    14183       +1     
  Misses         4260     4260              
- Partials        558      559       +1     

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