libstagefright: Ignore port settings changed event in certain cases

Ignore port settings changed event if the client has already
requested the component to move to Idle state (or any other state)
from Executing state. This scenario happens when Stop is called
immediately after Stop on OMXCodec. Since, Stop is called
so we request the component to move into Idle state and set
the state variable accordingly. In this case we might receive
port settings changed event after we have requested the
component to move into Idle state.

Change-Id: I3c2a8198b3906881ca1b41fece7f6e471fe2888c