fixed backspace; backspace bring back to uid if passord is empty

main.ino

     }
     else if (key == 'C' || key == '*') {
         if (len > 0) {
-            str = str.substring(0, len - 2);
+            str = str.substring(0, len - 1);
+            return true;
+        }
+        else if (status == Password) {
+            status = Uid;
             return true;
         }
     }