fix(ibus): drop a context on the Service.Destroy libibus really sends

libibus destroys an input context with Destroy on
org.freedesktop.IBus.Service, not on the InputContext interface, so the
call went unanswered and the context slot stayed taken until the whole
connection closed. A long-lived GTK process that opens and closes text
widgets exhausted the 1024 slots and then got LimitsExceeded for every
new field. The live contract test now destroys a context that way and
checks the path is gone.

ibus.c

@@ -854,6 +854,10 @@ onmsg(DBusConnection *c, DBusMessage *m, void*)
 		if(strcmp(member, "GetAll") == 0)
 			return handlepropertygetall(c, m);
 	}
+	/* libibus destroys a context through its Service base interface. */
+	if(strcmp(iface, "org.freedesktop.IBus.Service") == 0 &&
+	   strcmp(member, "Destroy") == 0)
+		iface = "org.freedesktop.IBus.InputContext";
 	if(strcmp(iface, "org.freedesktop.IBus.InputContext") == 0){
 		ctx = findcontext(c, path);
 		if(ctx == nil)