Fix T75470: File overwrite warning for UV Layout export

Referenced by issue blender/blender#75470, "export UV layout" doesn't warn if same name used.

io_mesh_uv_layout/__init__.py

@@ -70,6 +70,11 @@ class ExportUVLayout(bpy.types.Operator):
         description="Export all UVs in this mesh (not just visible ones)",
         default=False,
     )
+    check_existing = BoolProperty(
+        name="Check Existing",
+        default=True,
+        options={'HIDDEN'},
+    )
     modified: BoolProperty(
         name="Modified",
         description="Exports UVs from the modified mesh",