Parse M905 args in Marlin_main.cpp

Marlin/Marlin_main.cpp

    */
   inline void gcode_M905() {
     stepper.synchronize();
-    stepper.advance_M905();
+    stepper.advance_M905(code_seen('K') ? code_value_float() : -1.0);
   }
 #endif
 

Marlin/stepper.cpp

 
 #if ENABLED(LIN_ADVANCE)
 
-  void Stepper::advance_M905() {
-    if (code_seen('K')) extruder_advance_k = code_value_float();
+  void Stepper::advance_M905(const float &k) {
+    if (k >= 0) extruder_advance_k = k;
     SERIAL_ECHO_START;
     SERIAL_ECHOPAIR("Advance factor: ", extruder_advance_k);
     SERIAL_EOL;

Marlin/stepper.h

     }
 
     #if ENABLED(LIN_ADVANCE)
-      void advance_M905();
+      void advance_M905(const float &k);
       FORCE_INLINE int get_advance_k() { return extruder_advance_k; }
     #endif