SDWebImage: Crash on [SDWebImageDownloaderOperation reset]_block_invoke

[X] I have read and understood the CONTRIBUTING guide [X] I have read the Documentation [X] I have searched for a similar issue in the project and found none

I got this crash twice. Unfortunately cannot reproduce it. Just can provide info from Fabric.

Issue Info

Info	Value
Platform Name	iOS
Platform Version	10.3.1
SDWebImage Version	4.0.0
Integration Method	Cocoapods
Xcode Version	Xcode 8.0
Repro rate	twice
Repro with demo prj	cannot reproduce
Demo project link	cannot reproduce

Issue Description and Steps

Crashed: com.hackemist.SDWebImageDownloaderOperationBarrierQueue EXC_BAD_ACCESS KERN_INVALID_ADDRESS 0x000000092a29beb8

0 libobjc.A.dylib 0x184424150 objc_msgSend + 16 1 SDWebImage 0x1013d31e0 __38-[SDWebImageDownloaderOperation reset]_block_invoke (SDWebImageDownloaderOperation.m:227) 2 libdispatch.dylib 0x1848669e0 _dispatch_call_block_and_release + 24 3 libdispatch.dylib 0x1848669a0 _dispatch_client_callout + 16 4 libdispatch.dylib 0x184878578 _dispatch_queue_concurrent_drain + 1372 5 libdispatch.dylib 0x18486a2d4 _dispatch_queue_invoke + 892 6 libdispatch.dylib 0x184876a50 _dispatch_root_queue_drain + 540 7 libdispatch.dylib 0x1848767d0 _dispatch_worker_thread3 + 124 8 libsystem_pthread.dylib 0x184a6f1d0 _pthread_wqthread + 1096 9 libsystem_pthread.dylib 0x184a6ed7c start_wqthread + 4

Also downloaded crashreport from Apple

- (void)reset {
    dispatch_barrier_async(self.barrierQueue, ^{
        [self.callbackBlocks removeAllObjects]; // crash is here
    });
    self.dataTask = nil;
    self.imageData = nil;
    if (self.ownedSession) {
        [self.ownedSession invalidateAndCancel];
        self.ownedSession = nil;
    }
}