fix(composable): prevent scrolling parent error with parent null

[mlmoravek]

Fixes #742

Proposed Changes

• add isDefined check for nextParent in getScrollingParent composable

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cefffc2) 54.32% compared to head (3451931) 54.32%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #794   +/-   ##
========================================
  Coverage    54.32%   54.32%           
========================================
  Files           31       31           
  Lines         1493     1493           
  Branches       530      531    +1     
========================================
  Hits           811      811           
  Misses         682      682           

Flag	Coverage Δ
oruga-next	54.32% <100.00%> (ø)

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