Fix a crash when reloading the JS bundle

Summary:
changelog: [iOS][Fixed] Fix a crash when reloading JS bundle

Do not crash if self is nil.

Reviewed By: blakef

Differential Revision: D43352039

fbshipit-source-id: dd53677ca152d4021e43ed8d0f1b51c071ca3365

React/CoreModules/RCTDevSplitBundleLoader.mm

@@ -63,10 +63,12 @@ RCT_EXPORT_METHOD(loadBundle
             return;
           }
           __typeof(self) strongSelf = weakSelf;
-          strongSelf->_loadScript(source);
-          RCTDevSettings *devSettings = [strongSelf->_moduleRegistry moduleForName:"RCTDevSettings"];
-          [devSettings setupHMRClientWithAdditionalBundleURL:source.url];
-          resolve(@YES);
+          if (strongSelf) {
+            strongSelf->_loadScript(source);
+            RCTDevSettings *devSettings = [strongSelf->_moduleRegistry moduleForName:"RCTDevSettings"];
+            [devSettings setupHMRClientWithAdditionalBundleURL:source.url];
+            resolve(@YES);
+          }
         }];
   }
 }