Stock icon (Qt): Missing break in switch (CID 1323928)

Add a "// Fall through" comment to squelch a Coverity warning. Hopefully
the regex described at

http://security.coverity.com/blog/2013/Sep/gimme-a-break.html

is case-insensitive.

Change-Id: I10be63a77ed1e5e0c8000bad0c1b8d08db8b0951
Reviewed-on: https://code.wireshark.org/review/10509
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>

ui/qt/stock_icon_tool_button.cpp

@@ -81,6 +81,7 @@ bool StockIconToolButton::event(QEvent *event)
     case QEvent::Leave:
         if (leave_timer_ > 0) killTimer(leave_timer_);
         leave_timer_ = 0;
+        // Fall through
     case QEvent::MouseButtonRelease:
         setIconMode();
         break;