Fix single nozzle fan (#13038)

Marlin/src/gcode/temperature/M106_M107.cpp

@@ -28,6 +28,13 @@
 #include "../../module/motion.h"
 #include "../../module/temperature.h"
 
+#if ENABLED(SINGLENOZZLE)
+  #define _ALT_P active_extruder
+  #define _CNT_P EXTRUDERS
+#else
+  #define _ALT_P MIN(active_extruder, FAN_COUNT - 1)
+  #define _CNT_P MIN(EXTRUDERS, FAN_COUNT)
+#endif
 
 /**
  * M106: Set Fan Speed
@@ -43,9 +50,9 @@
  *           3-255 = Set the speed for use with T2
  */
 void GcodeSuite::M106() {
-  const uint8_t p = parser.byteval('P', MIN(active_extruder, FAN_COUNT - 1));
+  const uint8_t p = parser.byteval('P', _ALT_P);
 
-  if (p < MIN(EXTRUDERS, FAN_COUNT)) {
+  if (p < _CNT_P) {
 
     #if ENABLED(EXTRA_FAN_SPEED)
       const uint16_t t = parser.intval('T');
@@ -63,7 +70,7 @@ void GcodeSuite::M106() {
  * M107: Fan Off
  */
 void GcodeSuite::M107() {
-  const uint8_t p = parser.byteval('P', MIN(active_extruder, FAN_COUNT - 1));
+  const uint8_t p = parser.byteval('P', _ALT_P);
   thermalManager.set_fan_speed(p, 0);
 }