fix(state): consider state checkpoint path is not a file

[JustinChengLZ]

What type of PR is this?

• Sometimes, we end up reading a directory which will cause a panic. This is to handle that case

What this PR does / why we need it:

Which issue(s) this PR fixes:

Special notes for your reviewer:

[codecov]

Codecov Report

❌ Patch coverage is 64.28571% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.90%. Comparing base (7bf6456) to head (659d6c0).
⚠️ Report is 128 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/util/general/file.go	70.00%	3 Missing and 3 partials ⚠️
...customcheckpointmanager/customcheckpointmanager.go	50.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1100      +/-   ##
==========================================
+ Coverage   60.85%   60.90%   +0.04%     
==========================================
  Files         739      739              
  Lines       69780    69806      +26     
==========================================
+ Hits        42467    42514      +47     
+ Misses      22549    22515      -34     
- Partials     4764     4777      +13     

Flag	Coverage Δ
unittest	60.90% <64.28%> (+0.04%)	⬆️

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