Properly copy attributes before modifying in JSQMessagesCollectionViewFlowLayout

[algrid]

Pull request checklist

• All tests pass. Demo project builds and runs.
• I have resolved any merge conflicts.
• I have followed the coding style, and reviewed the contributing guidelines. Confirmation: ____

This fixes issue #1218

What's in this pull request?

Ensure that attributes array is properly copied before modification.
Could also fix #1424 but I'm not sure about that.

[codecov-io]

Current coverage is 61.27% (diff: 50.00%)

Merging #1868 into develop will not change coverage

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[jessesquires]

Thanks @algrid !

Based on the discussion in #1218 -- I'm not completely sure how a deep copy resolves this. Can you explain more? Do you have before/after repro steps?

[algrid]

@jessesquires I can reproduce the original problem in the demo app:

1. Turn on 'Springy bubbles' in Setting
2. Push via storyboard
3. Start scrolling

I get the following in my console:

2016-10-17 22:46:49.101 JSQMessages[5042:411339] Logging only once for UICollectionViewFlowLayout cache mismatched frame
2016-10-17 22:46:49.102 JSQMessages[5042:411339] UICollectionViewFlowLayout has cached frame mismatch for index path <NSIndexPath: 0xc000000004200016> {length = 2, path = 0 - 33} - cached value: {{4, 3421}, {367, 143}}; expected value: {{4, 3423}, {367, 143}}
2016-10-17 22:46:49.102 JSQMessages[5042:411339] This is likely occurring because the flow layout subclass JSQMessagesCollectionViewFlowLayout is modifying attributes returned by UICollectionViewFlowLayout without copying them

With this PR the problem is gone.

I'm doing here exactly what the log message suggests - don't modify attributes returned by UICollectionViewFlowLayout, instead make copies. Inspired by this: http://stackoverflow.com/a/33172179

[jessesquires]

Thanks @algrid ! 💯