CAM: fix rrf postprocessor always writing to "-" instead of specified file

src/Mod/CAM/Path/Post/scripts/rrf_post.py

@@ -35,6 +35,7 @@ import Path
 import Path.Base.Util as PathUtil
 import Path.Post.Utils as PostUtils
 import PathScripts.PathUtils as PathUtils
+from builtins import open as pyopen
 
 Revised = "2021-10-21"  # Revision date for this file.
 
@@ -443,8 +444,12 @@ def export(objectslist, filename, argstring):
     print("Done postprocessing.")
 
     # Write the file:
-    with open(filename, "w") as fp:
-        fp.write(final)
+    if not filename == "-":
+        gfile = pyopen(filename, "w")
+        gfile.write(final)
+        gfile.close()
+
+    return final
 
 
 def linenumber():