Fix rig_get_function_ptr return value

https://github.com/Hamlib/Hamlib/issues/502

src/misc.c

@@ -2073,13 +2073,13 @@ void *rig_get_function_ptr(rig_model_t rig_model,
 
     default:
         rig_debug(RIG_DEBUG_ERR, "Unknown function?? function=%d\n", rig_function);
-        return NULL;
-
     }
 
-    return RIG_OK;
+    return NULL;
 }
 
+// negative return indicates error
+// watch out for integer values that may be negative
 int rig_get_caps_int(rig_model_t rig_model, enum rig_caps_int_e rig_caps)
 {
     const struct rig_caps *caps = rig_get_caps(rig_model);
@@ -2102,8 +2102,6 @@ int rig_get_caps_int(rig_model_t rig_model, enum rig_caps_int_e rig_caps)
         rig_debug(RIG_DEBUG_ERR, "%s: Unknown rig_caps value=%d\n", __func__, rig_caps);
         return -RIG_EINVAL;
     }
-
-    return RIG_OK;
 }
 
 const char *rig_get_caps_cptr(rig_model_t rig_model,