Fix extruder stops extruding with LA (#11758)

Marlin/src/module/stepper.cpp

@@ -1485,16 +1485,10 @@ uint32_t Stepper::stepper_block_phase_isr() {
 
         #if ENABLED(LIN_ADVANCE)
           if (LA_use_advance_lead) {
-            // Wake up eISR on first acceleration loop and fire ISR if final adv_rate is reached
-            if (step_events_completed == steps_per_isr || (LA_steps && LA_isr_rate != current_block->advance_speed)) {
-              nextAdvanceISR = 0;
-              LA_isr_rate = current_block->advance_speed;
-            }
-          }
-          else {
-            LA_isr_rate = LA_ADV_NEVER;
-            if (LA_steps) nextAdvanceISR = 0;
+            // Fire ISR if final adv_rate is reached
+            if (LA_steps && LA_isr_rate != current_block->advance_speed) nextAdvanceISR = 0;
           }
+          else if (LA_steps) nextAdvanceISR = 0;
         #endif // LIN_ADVANCE
       }
       // Are we in Deceleration phase ?
@@ -1536,17 +1530,13 @@ uint32_t Stepper::stepper_block_phase_isr() {
 
         #if ENABLED(LIN_ADVANCE)
           if (LA_use_advance_lead) {
-            if (step_events_completed <= decelerate_after + steps_per_isr ||
-               (LA_steps && LA_isr_rate != current_block->advance_speed)
-            ) {
-              nextAdvanceISR = 0; // Wake up eISR on first deceleration loop
+            // Wake up eISR on first deceleration loop and fire ISR if final adv_rate is reached
+            if (step_events_completed <= decelerate_after + steps_per_isr || (LA_steps && LA_isr_rate != current_block->advance_speed)) {
+              nextAdvanceISR = 0;
               LA_isr_rate = current_block->advance_speed;
             }
           }
-          else {
-            LA_isr_rate = LA_ADV_NEVER;
-            if (LA_steps) nextAdvanceISR = 0;
-          }
+          else if (LA_steps) nextAdvanceISR = 0;
         #endif // LIN_ADVANCE
       }
       // We must be in cruise phase otherwise
@@ -1726,7 +1716,11 @@ uint32_t Stepper::stepper_block_phase_isr() {
         if ((LA_use_advance_lead = current_block->use_advance_lead)) {
           LA_final_adv_steps = current_block->final_adv_steps;
           LA_max_adv_steps = current_block->max_adv_steps;
+          //Start the ISR
+          nextAdvanceISR = 0;
+          LA_isr_rate = current_block->advance_speed;
         }
+        else LA_isr_rate = LA_ADV_NEVER;
       #endif
 
       if (current_block->direction_bits != last_direction_bits