Add input validation to longest subarray sum algorithm

[MayankSharma-2812]

Improves robustness by validating inputs and handling empty arrays while preserving the existing sliding window logic.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.85%. Comparing base (08d8c6b) to head (b9fd4f8).

Files with missing lines	Patch %	Lines
Sliding-Windows/LongestSubarrayWithSumAtMost.js	62.50%	6 Missing ⚠️
Search/BinarySearch.js	66.66%	4 Missing ⚠️
Sorts/BubbleSort.js	82.60%	4 Missing ⚠️
Sorts/SelectionSort.js	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1877      +/-   ##
==========================================
- Coverage   85.91%   85.85%   -0.07%     
==========================================
  Files         379      379              
  Lines       19778    19805      +27     
  Branches     3015     3032      +17     
==========================================
+ Hits        16993    17004      +11     
- Misses       2785     2801      +16     

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