Fix Dual X software endstops

Marlin/Marlin_main.cpp

@@ -1349,25 +1349,33 @@ void update_software_endstops(AxisEnum axis) {
   float offs = LOGICAL_POSITION(0, axis);
 
   #if ENABLED(DUAL_X_CARRIAGE)
+    bool did_update = false;
     if (axis == X_AXIS) {
+
+      // In Dual X mode hotend_offset[X] is T1's home position
       float dual_max_x = max(hotend_offset[X_AXIS][1], X2_MAX_POS);
+
       if (active_extruder != 0) {
+        // T1 can move from X2_MIN_POS to X2_MAX_POS or X2 home position (whichever is larger)
         soft_endstop_min[X_AXIS] = X2_MIN_POS + offs;
         soft_endstop_max[X_AXIS] = dual_max_x + offs;
-        return;
       }
       else if (dual_x_carriage_mode == DXC_DUPLICATION_MODE) {
+        // In Duplication Mode, T0 can move as far left as X_MIN_POS
+        // but not so far to the right that T1 would move past the end
         soft_endstop_min[X_AXIS] = base_min_pos(X_AXIS) + offs;
         soft_endstop_max[X_AXIS] = min(base_max_pos(X_AXIS), dual_max_x - duplicate_extruder_x_offset) + offs;
-        return;
+      }
+      else {
+        // In other modes, T0 can move from X_MIN_POS to X_MAX_POS
+        soft_endstop_min[axis] = base_min_pos(axis) + offs;
+        soft_endstop_max[axis] = base_max_pos(axis) + offs;
       }
     }
-    else
+  #else
-  #endif
-  {
     soft_endstop_min[axis] = base_min_pos(axis) + offs;
     soft_endstop_max[axis] = base_max_pos(axis) + offs;
-  }
+  #endif
 
   #if ENABLED(DEBUG_LEVELING_FEATURE)
     if (DEBUGGING(LEVELING)) {