Discovered a rare exception crasher under many images de-queueing at once.

[andre-wolfe]

0  CoreFoundation    0x18e2251b8 __exceptionPreprocess
1  libobjc.A.dylib   0x18cc5c55c objc_exception_throw
2  CoreFoundation    0x18e224c00 -[NSException name]
3  CoreFoundation    0x18e1110f8 -[NSArray indexOfObject:]
4  My App            0x1000db5b4 -[RemoteImageView cancel] (RemoteImageView.m:216)
5  My App            0x1000db458 __31-[RemoteImageView setImageURL:]_block_invoke
(RemoteImageView.m:196)

Exception Thrown: *** Collection <__NSArrayM: 0x170a58840> was mutated while being enumerated.

[andre-wolfe]

Added branch with pull request.