Planner anti-stutter by Sebastian Popp

Marlin/src/module/planner.h

@@ -534,6 +534,16 @@ class Planner {
     static block_t* get_current_block() {
       if (blocks_queued()) {
         block_t * const block = &block_buffer[block_buffer_tail];
+
+        // If the block has no trapezoid calculated, it's unsafe to execute.
+        if (movesplanned() > 1) {
+          const block_t * const next = &block_buffer[next_block_index(block_buffer_tail)];
+          if (TEST(block->flag, BLOCK_BIT_RECALCULATE) || TEST(next->flag, BLOCK_BIT_RECALCULATE))
+            return NULL;
+        }
+        else if (TEST(block->flag, BLOCK_BIT_RECALCULATE))
+          return NULL;
+
         #if ENABLED(ULTRA_LCD)
           block_buffer_runtime_us -= block->segment_time_us; // We can't be sure how long an active block will take, so don't count it.
         #endif