Protect core clip keyframes from being empty when Json is set

[jonoomph]

Protect core clip keyframes from being empty after loading from JSON (scale_x/y, location_x/y, origin_x/y, shear_x/y, rotation)

[jonoomph]

Deleting all keyframes makes clip disappear (instead of restoring defaults)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.89%. Comparing base (7793233) to head (503bbcb).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1046      +/-   ##
===========================================
+ Coverage    64.62%   64.89%   +0.27%     
===========================================
  Files          208      208              
  Lines        23491    23555      +64     
===========================================
+ Hits         15180    15286     +106     
+ Misses        8311     8269      -42     

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