Flickable: Cancel interaction on interactive changes

Otherwise if you have a listview with a flickable inside with a mouseare inside
the pressed is never set to false if you make the interactive property of the
outer list depend on the moving of the inner flickable. This makes that when
later you change currentIndex of the list and you have
StrictlyEnforceRange set, the list won't move because it still thinks it is pressed

Change-Id: I2c2021f486fc0a31840c3f2199bc7cb76dc01e3e
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>
Don't dereference null pointer.

Task-number: QTBUG-40448
Change-Id: I75eb886ae765191101d6b01ebd038211e5fe8fba
Reviewed-by: Lars Knoll <lars.knoll@digia.com>