qemu: Wait for monitor socket even without pid

If qemuMonitorOpenUnix is called without a related pid, i.e. for
QMP probing, a connect failure can happen as the result of a race.
Without a pid there is no retry and thus we give up too early.
This changes the code to retry if no pid is supplied.
Signed-off-by: NViktor Mihajlovski <mihajlov@linux.vnet.ibm.com>

src/qemu/qemu_monitor.c

@@ -283,7 +283,7 @@ qemuMonitorOpenUnix(const char *monitor, pid_t cpid)
             break;
 
         if ((errno == ENOENT || errno == ECONNREFUSED) &&
-            cpid && virProcessKill(cpid, 0) == 0) {
+            (!cpid || virProcessKill(cpid, 0) == 0)) {
             /* ENOENT       : Socket may not have shown up yet
              * ECONNREFUSED : Leftover socket hasn't been removed yet */
             continue;