core: Don't use a deallocated mutex for early-cancelled messages
core: Don't use a deallocated mutex for early-cancelled messages

In the case that a message is cancelled before it's queued in the session
(i.e. the cancellation callback is called immediately by
g_cancellable_connect()), ensure we don't free the mutex which we later
attempt to lock.

Distrotech/libgdata,GNOME/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Distrotech/libgdata,pwithnall/libgdata,pwithnall/libgdata,Distrotech/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata