Fix the possibility to delete nothing in list

src/android/org/linphone/ui/ListSelectionHelper.java

@@ -64,10 +64,12 @@ public class ListSelectionHelper {
 		mEditButton.setOnClickListener(new View.OnClickListener() {
 			@Override
 			public void onClick(View v) {
+				if (mAdapter.getCount() > 0) {
 					mAdapter.enableEdition(true);
 					mTopBar.setVisibility(View.GONE);
 					mEditTopBar.setVisibility(View.VISIBLE);
 				}
+			}
 		});
 
 		mSelectAllButton = view.findViewById(R.id.select_all);