Change tearDownReactContext ordering to prevent null assertion

Summary:
In `tearDownReactContext`, `reactContext.destroy()` sets `mCatalystInstance` to null. We cannot call `reactContext.getCatalystInstance()` after that without hitting an assertion. Change ordering so that doesn't happen in reload or teardown.

Changelog: [Internal]

Reviewed By: makovkastar

Differential Revision: D18041279

fbshipit-source-id: 22658dc506b76cf58aee1008841abacfe9410c9d

Author: JoshuaGross

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -1126,9 +1126,12 @@ private void tearDownReactContext(ReactContext reactContext) {
       }
     }
 
+    // Remove memory pressure listener before tearing down react context
+    // We cannot access the CatalystInstance after destroying the ReactContext.
+    mMemoryPressureRouter.removeMemoryPressureListener(reactContext.getCatalystInstance());
+
     reactContext.destroy();
     mDevSupportManager.onReactInstanceDestroyed(reactContext);
-    mMemoryPressureRouter.removeMemoryPressureListener(reactContext.getCatalystInstance());
   }
 
   /** @return instance of {@link ReactContext} configured a {@link CatalystInstance} set */