0026219: ShapeUpgrade_UnifySameDomain fails with StdFail_NotDone exception

Avoid merging edges if the collapsed vertex has a third connected edge.
Fix the problem when merged edges have different location.
Test case for issue CR26219

Additional fix to improve robustness.

Test cases for issue CR26219

Small correction of test cases for issue CR26219

src/BRepOffsetAPI/BRepOffsetAPI_MiddlePath.cxx

@@ -389,7 +389,10 @@ void BRepOffsetAPI_MiddlePath::Build()
         break;
       }
     }
-    myPaths.Append(Edges);
+    if (!Edges.IsEmpty())
+      myPaths.Append(Edges);
+    else
+      return;
   }
 
   //Filling of "myPaths"