Add rig backends in 0 range (maingly FlRig and rigctld) to targetable_ptt -- should avoid some vfo swapping going on

https://github.com/Hamlib/Hamlib/issues/836

src/rig.c

@@ -3281,13 +3281,13 @@ int HAMLIB_API rig_get_ptt(RIG *rig, vfo_t vfo, ptt_t *ptt)
         switch (backend_num)
         {
         // most rigs have only one PTT VFO so we can set that flag here
+        case 0:
         case RIG_ICOM:
         case RIG_KENWOOD:
         case RIG_YAESU:
             targetable_ptt = 1;
         }
 
-
         if (!targetable_ptt)
         {
             retcode = caps->set_vfo(rig, vfo);