ASTextNode2 crashes when used with transitionLayout shouldMeasureAsync:true

[jinlee]

Crash output:

0   CoreFoundation     0x000000010506212b __exceptionPreprocess + 171
1   libobjc.A.dylib    0x00000001046f6f41 objc_exception_throw + 48
2   CoreFoundation     0x00000001050672f2 +[NSException raise:format:arguments:] + 98
3   Foundation         0x0000000104197d69 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 193
4   AsyncDisplayKit    0x0000000103bb99e2 -[ASDisplayNode(UIViewBridge) backgroundColor] + 418
5   AsyncDisplayKit    0x0000000103d221df -[ASTextNode2 prepareAttributedStringForDrawing:] + 463
6   AsyncDisplayKit    0x0000000103d213ec -[ASTextNode2 calculateSizeThatFits:] + 1052

So the flow for calculating size that fits for ASTextNode2 is currently the following:

• calculateSizeThatFits relies on prepareAttributedStringForDrawing
• prepareAttributedStringForDrawing reads backgroundColor (it's not clear to me why this is required)
• backgroundColor asserts ASDisplayNodeAssertThreadAffinity

This is an issue when using transitionLayout(animated: true, shouldMeasureAsync: true).

I've played around with commenting out the color handling in prepareAttributedStringForDrawing and I've found that this fixes the issue.