android: don't crash if the user presses HOME while the loading screen is showing, this shuld also be made canceleable later

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@28530 a1c6a512-1295-4272-9138-f99709370657
diff --git a/android/src/org/rockbox/RockboxActivity.java b/android/src/org/rockbox/RockboxActivity.java
index 06ceb9c..47ea6c0 100644
--- a/android/src/org/rockbox/RockboxActivity.java
+++ b/android/src/org/rockbox/RockboxActivity.java
@@ -131,21 +131,24 @@
     protected void onPause() 
     {
         super.onPause();
-        rbservice.set_activity(null);
+        if (rbservice != null)
+        	rbservice.set_activity(null);
     }
     
     @Override
     protected void onStop() 
     {
         super.onStop();
-        rbservice.set_activity(null);
+        if (rbservice != null)
+        	rbservice.set_activity(null);
     }
     
     @Override
     protected void onDestroy() 
     {
         super.onDestroy();
-        rbservice.set_activity(null);
+        if (rbservice != null)
+        	rbservice.set_activity(null);
     }
 
     private void LOG(CharSequence text)