Fix #121751: Free CurvesTransformData on no selection

A `CurvesTransformData` is created to store transform points, but it's
not deleted when there's nothing selected, causing memory leak. Now
fixed.

Pull Request: https://projects.blender.org/blender/blender/pulls/121767

source/blender/editors/transform/transform_convert_curves.cc

@@ -177,6 +177,9 @@ static void createTransCurvesVerts(bContext * /*C*/, TransInfo *t)
       tc.data = MEM_cnew_array<TransData>(tc.data_len, __func__);
       curves_transform_data->positions.reinitialize(tc.data_len);
     }
+    else {
+      tc.custom.type.free_cb(t, &tc, &tc.custom.type);
+    }
   }
 
   /* Populate TransData structs. */