i965: Ignore execution mask for the mov(m0, g0) of VS URB write header on SNB.

Otherwise, we may not get the FFTID set up which would break freeing
of resources.

src/mesa/drivers/dri/i965/brw_eu_emit.c

@@ -1416,7 +1416,10 @@ void brw_urb_WRITE(struct brw_compile *p,
     * and the first message register index comes from src0.
     */
    if (intel->gen >= 6) {
+      brw_push_insn_state(p);
+      brw_set_mask_control( p, BRW_MASK_DISABLE );
       brw_MOV(p, brw_message_reg(msg_reg_nr), src0);
+      brw_pop_insn_state(p);
       src0 = brw_message_reg(msg_reg_nr);
    }