Change return type of layer_switch_get_layer() to uint8_t (#5011)

* Change return type of layer_switch_get_layer() to uint8_t

* Keep loop index signed so we don't wrap around

tmk_core/common/action_layer.c

@@ -296,7 +296,7 @@ action_t store_or_get_action(bool pressed, keypos_t key) {
  *
  * Gets the layer based on key info
  */
-int8_t layer_switch_get_layer(keypos_t key) {
+uint8_t layer_switch_get_layer(keypos_t key) {
 #ifndef NO_ACTION_LAYER
   action_t action;
   action.code = ACTION_TRANSPARENT;

tmk_core/common/action_layer.h

@@ -97,7 +97,7 @@ uint8_t read_source_layers_cache(keypos_t key);
 action_t store_or_get_action(bool pressed, keypos_t key);
 
 /* return the topmost non-transparent layer currently associated with key */
-int8_t layer_switch_get_layer(keypos_t key);
+uint8_t layer_switch_get_layer(keypos_t key);
 
 /* return action depending on current layer status */
 action_t layer_switch_get_action(keypos_t key);