Fix failure of 2nd rig_init call

Issue #735 is still fixed
https://github.com/Hamlib/Hamlib/issues/735
https://github.com/Hamlib/Hamlib/issues/1081

src/register.c

@@ -305,12 +305,14 @@ int HAMLIB_API rig_check_backend(rig_model_t rig_model)
         if (rig_hash_table[i]) { ++n; }
     }
 
+#if 0 // this stopped a 2nd rig_init call with a valid model to fail -- reversing
     if (n > 1)
     {
         rig_debug(RIG_DEBUG_ERR, "%s: rig model %u not found and rig count=%d\n",
                   __func__, rig_model, n);
         return -RIG_ENAVAIL;
     }
+#endif
 
     be_idx = rig_lookup_backend(rig_model);