No error on T0 with single-extruder and fix MIXING_EXTRUDER virtual tools (#12375)

Marlin/src/module/tool_change.cpp

@@ -498,11 +498,7 @@ inline void invalid_extruder_error(const uint8_t e) {
  * previous tool out of the way and the new tool into place.
  */
 void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool no_move/*=false*/) {
-  #if EXTRUDERS < 2
+  #if ENABLED(MIXING_EXTRUDER) && MIXING_VIRTUAL_TOOLS > 1
-
-    return invalid_extruder_error(tmp_extruder);
-
-  #elif ENABLED(MIXING_EXTRUDER) && MIXING_VIRTUAL_TOOLS > 1
 
       if (tmp_extruder >= MIXING_VIRTUAL_TOOLS)
         return invalid_extruder_error(tmp_extruder);
@@ -511,6 +507,11 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
       UNUSED(fr_mm_s);
       UNUSED(no_move);
 
+  #elif EXTRUDERS < 2
+
+    if (tmp_extruder) invalid_extruder_error(tmp_extruder);
+    return;
+
   #else
 
     #if DISABLED(MIXING_EXTRUDER)