implement G26 changes per review

Marlin/G26_Mesh_Validation_Tool.cpp

@@ -178,7 +178,7 @@
    * nozzle in a problem area and doing a G29 P4 R command.
    */
   void gcode_G26() {
-    SERIAL_ECHOLNPGM("G26 command started.  Waiting on heater(s).");
+    SERIAL_ECHOLNPGM("G26 command started.  Waiting for heater(s).");
     float tmp, start_angle, end_angle;
     int   i, xi, yi;
     mesh_index_pair location;
@@ -775,11 +775,11 @@
       #endif
           ubl.has_control_of_lcd_panel = true;
           thermalManager.setTargetBed(bed_temp);
-          next = millis() + 5000;
+          next = millis() + 5000UL;
           while (abs(thermalManager.degBed() - bed_temp) > 3) {
             if (ubl_lcd_clicked()) return exit_from_g26();
-            if (millis() > next) {
+            if (PENDING(millis(), next)) {
-              next = millis() + 5000;
+              next = millis() + 5000UL;
               print_heaterstates();
             }
             idle();
@@ -795,8 +795,8 @@
     thermalManager.setTargetHotend(hotend_temp, 0);
     while (abs(thermalManager.degHotend(0) - hotend_temp) > 3) {
       if (ubl_lcd_clicked()) return exit_from_g26();
-      if (millis() > next) {
+      if (PENDING(millis(), next)) {
-        next = millis() + 5000;
+        next = millis() + 5000UL;
         print_heaterstates();
       }
       idle();