Fixed alert dialog for not loaded libraries on Android being cancelable.

If the alert dialog could be canceled the Activity would not be finished here.
Also setting the property to "true" would be redundant because that is default.

android-project/src/org/libsdl/app/SDLActivity.java

@@ -132,7 +132,7 @@ public class SDLActivity extends Activity {
                         SDLActivity.mSingleton.finish();
                     }
                 });
-           dlgAlert.setCancelable(true);
+           dlgAlert.setCancelable(false);
            dlgAlert.create().show();
 
            return;