Added a check when searching for position of header, that the header found is visible.

Author: John Gray

library/src/main/java/com/timehop/stickyheadersrecyclerview/StickyRecyclerHeadersAdapter.java

@@ -36,4 +36,6 @@ public interface StickyRecyclerHeadersAdapter<VH extends RecyclerView.ViewHolder
    * @return the number of views in the adapter
    */
   int getItemCount();
+
+  boolean isPositionVisible(final int position);
 }

library/src/main/java/com/timehop/stickyheadersrecyclerview/StickyRecyclerHeadersDecoration.java

@@ -130,7 +130,10 @@ public int findHeaderPositionUnder(int x, int y) {
     for (int i = 0; i < mHeaderRects.size(); i++) {
       Rect rect = mHeaderRects.get(mHeaderRects.keyAt(i));
       if (rect.contains(x, y)) {
-        return mHeaderRects.keyAt(i);
+        int position = mHeaderRects.keyAt(i);
+        if (mAdapter.isPositionVisible(position)) {
+          return position;
+        }
       }
     }
     return -1;