Enhance LinearSearch with null check for value

[AbhiramSakha]

Fixes #7348

Changes made:

• Added null check for input array
• Handled empty array case
• Added null check for search value
• Prevented NullPointerException by checking array elements

Result:

Improved robustness and stability of LinearSearch implementation

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.43%. Comparing base (f38d5cd) to head (5af4613).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/searches/LinearSearch.java	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7355      +/-   ##
============================================
- Coverage     79.44%   79.43%   -0.01%     
- Complexity     7114     7115       +1     
============================================
  Files           793      793              
  Lines         23273    23273              
  Branches       4583     4583              
============================================
- Hits          18489    18487       -2     
- Misses         4046     4047       +1     
- Partials        738      739       +1     

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