Use the extruder argument in plan_buffer_line

Marlin/planner.cpp

 
   #ifdef PREVENT_DANGEROUS_EXTRUDE
     if (de) {
-      if (degHotend(active_extruder) < extrude_min_temp) {
+      if (degHotend(extruder) < extrude_min_temp) {
         position[E_AXIS] = target[E_AXIS]; // Behave as if the move really took place, but ignore E part
         de = 0; // no difference
         SERIAL_ECHO_START;
 
   block->steps[Z_AXIS] = labs(dz);
   block->steps[E_AXIS] = labs(de);
-  block->steps[E_AXIS] *= volumetric_multiplier[active_extruder];
-  block->steps[E_AXIS] *= extruder_multiply[active_extruder];
+  block->steps[E_AXIS] *= volumetric_multiplier[extruder];
+  block->steps[E_AXIS] *= extruder_multiply[extruder];
   block->steps[E_AXIS] /= 100;
   block->step_event_count = max(block->steps[X_AXIS], max(block->steps[Y_AXIS], max(block->steps[Z_AXIS], block->steps[E_AXIS])));
 
     delta_mm[Y_AXIS] = dy / axis_steps_per_unit[Y_AXIS];
   #endif
   delta_mm[Z_AXIS] = dz / axis_steps_per_unit[Z_AXIS];
-  delta_mm[E_AXIS] = (de / axis_steps_per_unit[E_AXIS]) * volumetric_multiplier[active_extruder] * extruder_multiply[active_extruder] / 100.0;
+  delta_mm[E_AXIS] = (de / axis_steps_per_unit[E_AXIS]) * volumetric_multiplier[extruder] * extruder_multiply[extruder] / 100.0;
 
   if (block->steps[X_AXIS] <= dropsegments && block->steps[Y_AXIS] <= dropsegments && block->steps[Z_AXIS] <= dropsegments) {
     block->millimeters = fabs(delta_mm[E_AXIS]);

Marlin/stepper.cpp

       TCCR0A &= ~BIT(WGM01);
       TCCR0A &= ~BIT(WGM00);
     #endif
-    e_steps[0] = 0;
-    e_steps[1] = 0;
-    e_steps[2] = 0;
-    e_steps[3] = 0;
+    e_steps[0] = e_steps[1] = e_steps[2] = e_steps[3] = 0;
     TIMSK0 |= BIT(OCIE0A);
   #endif //ADVANCE