clamp subview index _after_ removing from superview

[rikner]

Type of change:

Motivation (current vs expected behavior)

314 revealed another bug, where the subview index was not correctly bound-checked and could therefore cause a crash.

Please check if the PR fulfills these requirements

• [x] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [x] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [x] The commit messages are clean and understandable
• [ ] Tests for the changes have been added (for bug fixes / features)

[codecov[bot]]

Codecov Report

Merging #323 (7cd12fa) into master (44f70d6) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #323   +/-   ##
=======================================
  Coverage   51.15%   51.15%           
=======================================
  Files          87       87           
  Lines        2895     2895           
=======================================
  Hits         1481     1481           
  Misses       1414     1414           

Impacted Files	Coverage Δ
Sources/UIView.swift	90.37% <100.00%> (ø)

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