Fix dropdown scrollbars (kallisti5#130)

* Use const in more places

* Revert "Use const in more places"

This reverts commit 125b4aa.

* Fixed dropdown scrollbars obstructing content

In some cases, the dropdown would show the scollbars on top of the content, obstructing it.
This was very apparent in cases where the content has only one entry, and the horizontal scrollbar is drawn on top of it, making it impossible to see or select that entry.

src/widgets/dropdown.cpp

@@ -414,11 +414,11 @@ namespace gcn
             else
             {
                 setHeight(listBoxHeight + h2 + 2);
-                mScrollArea->setHeight(listBoxHeight);
+                mScrollArea->setHeight(listBoxHeight + mScrollArea->getScrollbarWidth());
             }
         }
 
-        mScrollArea->setWidth(getWidth());
+        mScrollArea->setWidth(getWidth() + mScrollArea->getScrollbarWidth());
         // Resize the ListBox to exactly fit the ScrollArea.
         mListBox->setWidth(mScrollArea->getChildrenArea().width);
         mScrollArea->setPosition(0, 0);