Handle user-provided OnScrollListeners

Otherwise, if a user passes one (for endless scrolling, for example),
our "pause" functionality breaks

EnhancedListView/src/main/java/de/timroes/android/listview/EnhancedListView.java

@@ -322,6 +322,8 @@ public void handleMessage(final Message msg) {
     private long mAnimationTime;
 
     private final Object[] mAnimationLock = new Object[0];
+
+    private OnScrollListener mUserScrollListener;
 
     // Swipe-To-Dismiss
     private boolean mSwipeEnabled;
@@ -355,6 +357,27 @@ public void handleMessage(final Message msg) {
     private Button mUndoButton;
     // END Swipe-To-Dismiss
 
+    private final OnScrollListener mScrollListener = new OnScrollListener() {
+
+        @Override
+        public void onScrollStateChanged(final AbsListView view, final int scrollState) {
+            mSwipePaused = scrollState == OnScrollListener.SCROLL_STATE_TOUCH_SCROLL;
+
+            // call through to user's listener
+            final OnScrollListener userScrollListener = mUserScrollListener;
+            if (userScrollListener != null)
+                userScrollListener.onScrollStateChanged(view, scrollState);
+        }
+
+        @Override
+        public void onScroll(final AbsListView view, final int firstVisibleItem,
+                final int visibleItemCount, final int totalItemCount) {
+            final OnScrollListener userScrollListener = mUserScrollListener;
+            if (userScrollListener != null)
+                userScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
+        }
+    };
+
     /**
      * {@inheritDoc}
      */
@@ -414,7 +437,7 @@ public boolean onTouch(final View v, final MotionEvent event) {
         mScreenDensity = getResources().getDisplayMetrics().density;
         // END initialize undo popup
 
-        setOnScrollListener(makeScrollListener());
+        super.setOnScrollListener(mScrollListener);
 
     }
 
@@ -453,6 +476,14 @@ public EnhancedListView disableSwipeToDismiss() {
         mSwipeEnabled = false;
         return this;
     }
+
+    @Override
+    public void setOnScrollListener(final OnScrollListener l) {
+        mUserScrollListener = l;
+
+        // call super again with ours so it gets fired as expected
+        super.setOnScrollListener(mScrollListener);
+    }
 
     /**
      * Sets the callback to be called when the user dismissed an item from the list (either by
@@ -928,19 +959,6 @@ private void changeButtonLabel() {
         mUndoButton.setText(msg);
     }
 
-    private OnScrollListener makeScrollListener() {
-        return new OnScrollListener() {
-            @Override
-            public void onScrollStateChanged(final AbsListView view, final int scrollState) {
-                mSwipePaused = scrollState == OnScrollListener.SCROLL_STATE_TOUCH_SCROLL;
-            }
-
-            @Override
-            public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount, final int totalItemCount) {
-            }
-        };
-    }
-
     /**
      * Checks whether the delta of a swipe indicates, that the swipe is in the
      * correct direction, regarding the direction set via