Fixed: Item.getSize sometimes throwing exception and application crashses.

[MohitMaliFtechiz]

Fixes #4157

Created an extension function to safely retrieve the item's size and handle any potential errors within this function. This method was used in three places, and since we are already handling cases where this method returns null, the existing functionality remains unaffected.

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.

Project coverage is 56.89%. Comparing base (7313a12) to head (98f29b7).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...org/kiwix/kiwixmobile/core/reader/ZimFileReader.kt	50.00%	3 Missing and 1 partial ⚠️
...iwix/kiwixmobile/core/reader/ZimReaderContainer.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4158      +/-   ##
============================================
- Coverage     56.96%   56.89%   -0.07%     
+ Complexity     1519     1516       -3     
============================================
  Files           313      313              
  Lines         13367    13373       +6     
  Branches       1655     1655              
============================================
- Hits           7614     7609       -5     
- Misses         4611     4618       +7     
- Partials       1142     1146       +4     

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