Minor patch ups to `G29`

This may fix a subtle bug caused by doing `G29` more than once without
`G28` between.

Marlin/Marlin_main.cpp

         //bedLevel.debug("bedLevel");
 
         //plan_bed_level_matrix.debug("bed level before");
-        //vector_3 uncorrected_position = plan_get_position_mm();
+        //vector_3 uncorrected_position = plan_get_position();
         //uncorrected_position.debug("position before");
 
         vector_3 corrected_position = plan_get_position();
 
     #endif // AUTO_BED_LEVELING_GRID
 
-    #if ENABLED(Z_PROBE_SLED)
-      dock_sled(false); // engage (un-dock) the Z probe
-    #elif ENABLED(Z_PROBE_ALLEN_KEY) || (ENABLED(DELTA) && SERVO_LEVELING)
-      deploy_z_probe();
-    #endif
-
-    st_synchronize();
-
     if (!dryrun) {
+
       // make sure the bed_level_rotation_matrix is identity or the planner will get it wrong
       plan_bed_level_matrix.set_to_identity();
 
       #if ENABLED(DELTA)
         reset_bed_level();
       #else //!DELTA
-        //vector_3 corrected_position = plan_get_position_mm();
+
         #if ENABLED(DEBUG_LEVELING_FEATURE)
           if (DEBUGGING(LEVELING)) DEBUG_POS("BEFORE matrix.set_to_identity", current_position);
         #endif
 
+        //vector_3 corrected_position = plan_get_position();
         //corrected_position.debug("position before G29");
         vector_3 uncorrected_position = plan_get_position();
         //uncorrected_position.debug("position during G29");
       #endif // !DELTA
     }
 
+    #if ENABLED(Z_PROBE_SLED)
+      dock_sled(false); // engage (un-dock) the Z probe
+    #elif ENABLED(Z_PROBE_ALLEN_KEY) || (ENABLED(DELTA) && SERVO_LEVELING)
+      deploy_z_probe();
+    #endif
+
+    st_synchronize();
+
     setup_for_endstop_move();
 
     feedrate = homing_feedrate[Z_AXIS];