Animate already loaded images when using gappless playback

[renefloor]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Bug fix

⤵️ What is the current behavior?

The image widget doesn't show the placeholder when the image is already loaded in memory.

🆕 What is the new behavior (if this is a feature change)?

The image widget does show the placeholder when the image is already loaded, but the placeholder is the previous image and gapless playback is enabled.

💥 Does this PR introduce a breaking change?

No

🐛 Recommendations for testing

Test in real life situations

📝 Links to relevant issues/docs

Fixes Baseflow/flutter_cached_network_image#625

🤔 Checklist before submitting

• All projects build
• Follows style guide lines
• Relevant documentation was updated
• Rebased onto current develop

[renefloor]

@Kavantix can you try if this fixes your issue? You should be able to test this with cachednetworkimage using dependency overrides.

[codecov]

Codecov Report

Merging #19 (577229b) into develop (a89e995) will decrease coverage by 2.95%.
The diff coverage is 0.00%.

❗ Current head 577229b differs from pull request most recent head d8c2bb2. Consider uploading reports for the commit d8c2bb2 to get more accurate results

@@             Coverage Diff             @@
##           develop      #19      +/-   ##
===========================================
- Coverage    46.38%   43.42%   -2.96%     
===========================================
  Files            8        8              
  Lines          235      251      +16     
===========================================
  Hits           109      109              
- Misses         126      142      +16     

Impacted Files	Coverage Δ
lib/src/image/fade_widget.dart	2.38% <0.00%> (-1.07%)	⬇️
lib/src/image/image.dart	46.37% <0.00%> (-2.11%)	⬇️
lib/src/image/image_handler.dart	61.79% <0.00%> (-0.71%)	⬇️
lib/src/errors.dart	33.33% <0.00%> (+2.08%)	⬆️

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[Kavantix]

Seems to work nicely! @renefloor