Partial Restore: ensure line segment length when x coordinate is exactly zero

fixes #4012

src/Mod/Part/App/Geometry.cpp

@@ -3752,7 +3752,13 @@ void GeomLineSegment::Restore    (Base::XMLReader &reader)
         // the points are too close. The best try to restore is incrementing the distance.
         // for other objects, the best effort may be just to leave default values.
         reader.setPartialRestore(true);
-        end = start + Base::Vector3d(start.x*DBL_EPSILON,0,0);
+
+        if(start.x == 0) {
+            end = start + Base::Vector3d(DBL_EPSILON,0,0);
+        }
+        else {
+            end = start + Base::Vector3d(start.x*DBL_EPSILON,0,0);
+        }
 
         setPoints(start, end);
     }