fix a crash while resizing
fix a crash while resizing

Change-Id: I6d7ada609bdaf13e39cccfd276b9a083462e63fa
Reviewed-on: http://cr.qtquick.me/891
Tested-by: http://ci.qtquick.me/
Reviewed-by: Takahiro Hashimoto <b59128e2582a625f3a4337ede555b631692b1b94@qtquick.me>
Tested-by: Takahiro Hashimoto <b59128e2582a625f3a4337ede555b631692b1b94@qtquick.me>
Tested-by: Tasuku Suzuki <42980d970444f9101663582e70cd53623b3238b4@gmail.com>
Reviewed-by: Tasuku Suzuki <42980d970444f9101663582e70cd53623b3238b4@gmail.com>

qt-users-jp/qimsys,qt-users-jp/qimsys,qt-users-jp/qimsys,qt-users-jp/qimsys