Fix stepper shutdown during waiting for temperatures

In the wait loops of M109 M190 idle() is called, what checks
stepper_inactive_time against previous_cmd_ms.
Because we can be several minutes inside the loop, resetting
previous_cmd_ms only outside the loop caused stepper shutdowns.

The name of previous_cmd_ms does not really reflect its use. It's set
not only when a new command was received or executed but also in many of
the movement routines. For that the little extension of using it during
the wait will (hopefully) not hurt.

# Conflicts:
#	Marlin/Configuration_adv.h

Marlin/Marlin_main.cpp

@@ -3975,6 +3975,7 @@ inline void gcode_M109() {
     }
 
     idle();
+    refresh_cmd_timeout(); // to prevent stepper_inactive_time from running out
 
     #ifdef TEMP_RESIDENCY_TIME
       // start/restart the TEMP_RESIDENCY_TIME timer whenever we reach target temp for the first time
@@ -3989,7 +3990,6 @@ inline void gcode_M109() {
   }
 
   LCD_MESSAGEPGM(MSG_HEATING_COMPLETE);
-  refresh_cmd_timeout();
   print_job_start_ms = previous_cmd_ms;
 }
 
@@ -4024,9 +4024,9 @@ inline void gcode_M109() {
         #endif
       }
       idle();
+      refresh_cmd_timeout(); // to prevent stepper_inactive_time from running out
     }
     LCD_MESSAGEPGM(MSG_BED_DONE);
-    refresh_cmd_timeout();
   }
 
 #endif // HAS_TEMP_BED