Don't execute completion block if cancelled

AFNetworking/AFHTTPRequestOperation.m

@@ -38,6 +38,10 @@
 {
     AFHTTPRequestOperation *operation = [[[self alloc] initWithRequest:urlRequest] autorelease];
     operation.completionBlock = ^ {
+        if ([operation isCancelled]) {
+            return;
+        }
+        
         if (operation.error) {
             if (failure) {
                 dispatch_async(dispatch_get_main_queue(), ^(void) {

AFNetworking/AFImageRequestOperation.m

@@ -53,6 +53,10 @@ static dispatch_queue_t image_request_operation_processing_queue() {
     AFImageRequestOperation *operation = [[[AFImageRequestOperation alloc] initWithRequest:urlRequest] autorelease];
     
     operation.completionBlock = ^ {
+        if ([operation isCancelled]) {
+            return;
+        }
+        
         dispatch_async(image_request_operation_processing_queue(), ^(void) {
             if (operation.error) {
                 if (failure) {

AFNetworking/AFURLConnectionOperation.m

@@ -274,6 +274,10 @@ static inline BOOL AFOperationStateTransitionIsValid(AFOperationState from, AFOp
 }
 
 - (void)cancel {
+    if ([self isFinished]) {
+        return;
+    }
+    
     [super cancel];
     
     self.cancelled = YES;
@@ -282,7 +286,7 @@ static inline BOOL AFOperationStateTransitionIsValid(AFOperationState from, AFOp
 }
 
 - (void)finish {
-    self.state = AFHTTPOperationFinishedState;    
+    self.state = AFHTTPOperationFinishedState;
 }
 
 #pragma mark - NSURLConnectionDelegate