ProgressBar: Fix error of process bar cannot update on some condition.

When onDetachedFromWindow in processbar, if flag mRefreshIsPosted is true,
we should set it to false. Otherwise, this flag will stay in true status,
cannot turn to false anymore. At that condition, processbar cannot get
update.

Change-Id: I14c4e976b165ad737aae0a403a44822a7b3b2422
Author: Liang Wang <liangx.wang@intel.com>
Signed-off-by: Liang Wang <liangx.wang@intel.com>
Signed-off-by: Bing Deng <bingx.deng@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 61090