Looping calls to update waveform time range can cause crash

[dredenba]

I have a couple of crashes reported where it looks like the SCScrollableWaveformView gets into a nasty loop when the KVO observing function changes the time range and then this somehow results in the observing function triggering again to update the scroll view which then triggers the observing function to trigger and update the waveform which changes the time range again.

Here is a chunk of the stack trace that started it (which then effectively repeats many many times before crashing):

0x1002bcc28 -SCScrollableWaveformView _updateWaveform
0x1002bcf7c -SCScrollableWaveformView observeValueForKeyPath:ofObject:change:context:

4113 Foundation 0x18499bf64 NSKeyValueNotifyObserver + 304
4114 Foundation 0x18499ba8c NSKeyValueDidChange + 404
4115 Foundation 0x184a461ac -[NSObject(NSKeyValueObservingPrivate) _changeValueForKeys:count:maybeOldValuesDict:usingBlock:] + 732
4116 Foundation 0x18499afc0 -[NSObject(NSKeyValueObservingPrivate) _changeValueForKey:key:key:usingBlock:] + 64
4117 Foundation 0x184a43b38 _NSSetPointValueAndNotify + 284

0x1002bce34 -SCScrollableWaveformView _updateScrollView
0x1002bcf7c -SCScrollableWaveformView observeValueForKeyPath:ofObject:change:context:

4120 Foundation 0x18499bf64 NSKeyValueNotifyObserver + 304
4121 Foundation 0x18499ba8c NSKeyValueDidChange + 404
4122 Foundation 0x184986624 -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 120

0x1002c01dc -SCWaveformView setTimeRange:

4124 CoreFoundation 0x1840a4a60 invoking_ + 144
4125 CoreFoundation 0x183f9c488 -[NSInvocation invoke] + 284
4126 Foundation 0x1849ad270 NSKVOForwardInvocation + 300
4127 CoreFoundation 0x1840a2a1c _forwarding_ + 408
4128 CoreFoundation 0x183fa0c5c _CF_forwarding_prep_0 + 92

0x1002bcc28 -SCScrollableWaveformView _updateWaveform
0x1002bcf7c -SCScrollableWaveformView observeValueForKeyPath:ofObject:change:context:

4131 Foundation 0x18499bf64 NSKeyValueNotifyObserver + 304
4132 Foundation 0x18499ba8c NSKeyValueDidChange + 404
4133 Foundation 0x184a461ac -[NSObject(NSKeyValueObservingPrivate) _changeValueForKeys:count:maybeOldValuesDict:usingBlock:] + 732
4134 Foundation 0x18499afc0 -[NSObject(NSKeyValueObservingPrivate) _changeValueForKey:key:key:usingBlock:] + 64
4135 Foundation 0x184a43b38 _NSSetPointValueAndNotify + 284
4136 UIKit 0x1893b8c54 -[UIScrollView _smoothScrollWithUpdateTime:] + 2400
`

Is anyone else encountering this problem?
I don't have direct steps to reproduce this problem but I have 3 reports in the last 2 days (two on iPhone 6 with iOS 9.3.4 and one on iPhone 6s with iOS 9.3.3).