FP2-1197: fix a crash issue in packageinstaller

Change-Id: I959e01e809590579f8e1474b4581c39a051e343a
FP2-1197: [ST_2][Monkey] 'com.android.packageinstaller' crash
diff --git a/src/com/android/packageinstaller/UninstallerActivity.java b/src/com/android/packageinstaller/UninstallerActivity.java
index 96bc993..50e7bbc 100755
--- a/src/com/android/packageinstaller/UninstallerActivity.java
+++ b/src/com/android/packageinstaller/UninstallerActivity.java
@@ -109,7 +109,9 @@
         @Override
         public void onDismiss(DialogInterface dialog) {
             super.onDismiss(dialog);
-            getActivity().finish();
+            Activity activity = getActivity();
+            if(activity != null)
+                activity.finish();
         }
     }