Allow barrett to program and unprogrammed channel

https://github.com/Hamlib/Hamlib/issues/923

rigs/barrett/950.c

@@ -202,7 +202,12 @@ int barrett950_set_freq(RIG *rig, vfo_t vfo, freq_t freq)
         return retval;
     }
 
-    if (sscanf(response, "%4d%8lf%8lf", &chan, &freq_rx, &freq_tx) != 3)
+    if (strstr(response,"E5"))
+    {
+        freq_rx = freq_tx = 0;
+        rig_debug(RIG_DEBUG_VERBOSE, "%s: new channel being programmed\n", __func__);
+    }
+    else if (sscanf(response, "%4d%8lf%8lf", &chan, &freq_rx, &freq_tx) != 3)
     {
         rig_debug(RIG_DEBUG_ERR, "%s: unable to parse chan/freq from %s\n", __func__,
                   response);