Fix_Error_when_parent_removed : DONE

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List which issues are fixed by this PR. You must list at least one issue.
Fix Red screen when popover parent is removed while popover is shown

Pre-launch Checklist

• I read and followed the Effective Dart.
• I listed at least one issue or feature that this PR fixes or adds in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I updated/added relevant documentation to README.md.
• I updated/added relevant code samples to example.
• I added new tests to check the change I am making or feature I am adding, or Minikin said the PR is test-exempt.
• All existing and new tests are passing.

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[codecov]

Codecov Report

Merging #43 (85b615a) into main (ef6a749) will decrease coverage by 0.22%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
- Coverage   91.18%   90.96%   -0.23%     
==========================================
  Files          11       11              
  Lines         454      454              
==========================================
- Hits          414      413       -1     
- Misses         40       41       +1     

Impacted Files	Coverage Δ
lib/src/popover.dart	75.00% <ø> (-2.78%)	⬇️
lib/src/popover_item.dart	80.59% <50.00%> (-0.95%)	⬇️

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