#268 Cancelled task should not trigger `then` promise function

ios/RNFetchBlobFS.m

         encoding = [encoding lowercaseString];
         if(![fm fileExistsAtPath:folder]) {
             [fm createDirectoryAtPath:folder withIntermediateDirectories:YES attributes:NULL error:&err];
-            [fm createFileAtPath:path contents:nil attributes:nil];
-        }
-        if(err != nil) {
-            reject(@"RNFetchBlob writeFile Error", @"could not create file at path", nil);
-            return;
+            if(err != nil) {
+                return reject(@"ENOTDIR", [NSString stringWithFormat:@"Failed to create parent directory of '%@'; error: %@", path, [err description]], nil);
+            }
+            if(![fm createFileAtPath:path contents:nil attributes:nil]) {
+                return reject(@"ENOENT", [NSString stringWithFormat:@"File '%@' does not exist and could not be created", path], nil);
+            }
         }
         NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:path];
         NSData * content = nil;

ios/RNFetchBlobNetwork.m

     }
 
     __block NSURLSessionDataTask * task = [session dataTaskWithRequest:req];
-    [taskTable setObject:task forKey:taskId];
+    
+    [taskTable setObject:@{ @"session" : task, @"isCancelled" : @NO } forKey:taskId];
     [task resume];
 
     // network status indicator
     {
         errMsg = [error localizedDescription];
     }
+    NSDictionary * taskSession = [taskTable objectForKey:taskId];
+    BOOL isCancelled = [taskSession valueForKey:@"isCancelled"];
+    if(isCancelled) {
+        errMsg = @"task cancelled";
+    }
 
     if(respFile == YES)
     {
 
 + (void) cancelRequest:(NSString *)taskId
 {
-    NSURLSessionDataTask * task = [taskTable objectForKey:taskId];
-    if(task != nil && task.state == NSURLSessionTaskStateRunning)
-        [task cancel];
+    NSDictionary * task = [taskTable objectForKey:taskId];
+    
+    if(task != nil) {
+        NSURLSessionDataTask * session = [task objectForKey:@"session"];
+        if(session.state == NSURLSessionTaskStateRunning) {
+            [task setValue:@NO forKey:@"isCancelled"];
+            [session cancel];
+        }
+    }
+    
 }