Fix currentActivity being null when launching Redbox

Summary:
Try to reuse currentActivity when the new context from "mReactInstanceDevHelper.getCurrentActivity()" is null to fix  "Unable to launch redbox because react activity is not available..."

Changelog:
[Android][Fixed] - Fix currentActivity being null when launching Redbox

Reviewed By: philIip

Differential Revision: D30942434

fbshipit-source-id: faf03390adc545376f3cec223eac5a16bf8233ea

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevSupportManagerBase.java

@@ -345,16 +345,21 @@ private void showNewError(
           @Override
           public void run() {
             Activity context = mReactInstanceDevHelper.getCurrentActivity();
-            if (mRedBoxDialog == null || context != currentActivity) {
-              if (context == null || context.isFinishing()) {
-                FLog.e(
-                    ReactConstants.TAG,
-                    "Unable to launch redbox because react activity "
-                        + "is not available, here is the error that redbox would've displayed: "
-                        + message);
-                return;
-              }
+            if (context != null && !context.isFinishing() && currentActivity != context) {
               currentActivity = context;
+              // Create a new RedBox when currentActivity get updated
+              mRedBoxDialog =
+                  new RedBoxDialog(currentActivity, DevSupportManagerBase.this, mRedBoxHandler);
+            }
+            if (currentActivity == null || currentActivity.isFinishing()) {
+              FLog.e(
+                  ReactConstants.TAG,
+                  "Unable to launch redbox because react activity "
+                      + "is not available, here is the error that redbox would've displayed: "
+                      + message);
+              return;
+            }
+            if (mRedBoxDialog == null) {
               mRedBoxDialog =
                   new RedBoxDialog(currentActivity, DevSupportManagerBase.this, mRedBoxHandler);
             }