Fixing MinObject related issues in MRDWrapper

[abhishek10004]

1. Ensure MRD's minObject is updated when inode's minObject is updated.

2. Ensure that we set MRD to nil if there were any errors while creating it. (We observed that NewMultiRangeDownloader returned a non nil value for MRD even in case of error)

b/391534052

[codecov]

Codecov Report

Attention: Patch coverage is 82.14286% with 5 lines in your changes missing coverage. Please review.

Project coverage is 75.28%. Comparing base (8e0388a) to head (ecc5619).
Report is 56 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/fs/inode/file.go	54.54%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2936      +/-   ##
==========================================
- Coverage   75.66%   75.28%   -0.39%     
==========================================
  Files         125      125              
  Lines       17641    17695      +54     
==========================================
- Hits        13348    13321      -27     
- Misses       3732     3810      +78     
- Partials      561      564       +3     

Flag	Coverage Δ
unittests	75.28% <82.14%> (-0.39%)	⬇️

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