fix crash in chat example
fix crash in chat example

Change-Id: I1634ed92c7376d16a55aa50c2f4838c8785ff205
Reviewed-on: http://cr.qtquick.me/550
Tested-by: http://ci.qtquick.me/
Tested-by: Kimitake San <9ff8b03522c239045a53d4799937539ed3fe4518@gmail.com>
Reviewed-by: Tasuku Suzuki <42980d970444f9101663582e70cd53623b3238b4@gmail.com>
Tested-by: Tasuku Suzuki <42980d970444f9101663582e70cd53623b3238b4@gmail.com>

qt-users-jp/silk,qt-users-jp/silk,yatsek/silk,yatsek/silk,yatsek/silk,qt-users-jp/silk,yatsek/silk,qt-users-jp/silk