planner.synchronize at start of tool_change

See https://github.com/MarlinFirmware/Marlin/issues/10949#issuecomment-398540498

Marlin/src/module/tool_change.cpp

  * previous tool out of the way and the new tool into place.
  */
 void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool no_move/*=false*/) {
+  planner.synchronize();
+
   #if ENABLED(MIXING_EXTRUDER) && MIXING_VIRTUAL_TOOLS > 1
 
     mixing_tool_change(tmp_extruder);