Surface: [skip ci] only try to build surface if at least two boundary curves are used

src/Mod/Surface/App/FeatureFilling.cpp

@@ -298,6 +298,7 @@ App::DocumentObjectExecReturn *Filling::execute(void)
         }
 
         // Add the constraints of border curves/faces (bound)
+        int numBoundaries = BoundaryEdges.getSize();
         addConstraints(builder, BoundaryEdges, BoundaryFaces, BoundaryOrder, Standard_True);
 
         // Add additional edge constraints if available (unbound)
@@ -316,7 +317,8 @@ App::DocumentObjectExecReturn *Filling::execute(void)
         }
 
         //Build the face
-        builder.Build();
+        if (numBoundaries > 1)
+            builder.Build();
         if (!builder.IsDone()) {
             Standard_Failure::Raise("Failed to create a face from constraints");
         }
@@ -327,7 +329,6 @@ App::DocumentObjectExecReturn *Filling::execute(void)
         return App::DocumentObject::StdReturn;
     }
     catch (Standard_Failure& e) {
-
         return new App::DocumentObjectExecReturn(e.GetMessageString());
     }
 }