Editor: fix selection path for empty selections

Especially targets the painting of empty snippet replacement placeholder
like in the default "if" snippet.

Change-Id: I42d9fb901c66cddf4eab9dd7275b42a8f4e81282
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/texteditoroverlay.cpp

@@ -134,8 +134,10 @@ QPainterPath TextEditorOverlay::createSelectionPath(const QTextCursor &begin, co
         int x = line.cursorToX(pos);
         lineRect.setLeft(x - borderWidth);
         lineRect.setRight(x + borderWidth);
+        lineRect.setBottom(lineRect.bottom() + borderWidth);
         QPainterPath path;
         path.addRect(lineRect);
+        path.translate(offset);
         return path;
     }