Refactor in SDWebImageManager

@@ -314,10 +314,11 @@
 }
 
 - (void)safelyRemoveOperationFromRunning:(nullable SDWebImageCombinedOperation*)operation {
+    if (!operation) {
+        return;
+    }
     LOCK(self.runningOperationsLock);
-    if (operation) {
     [self.runningOperations removeObject:operation];
-    }
     UNLOCK(self.runningOperationsLock);
 }