Capturing sys.stdout too early breaks pytest capfd

Since at least testing and possibly users may update
sys.stdout after importing the module, we defer the
evaluation of `sys.stdout` until the last possible
opportunity.

src/omero_rdf/__init__.py

@@ -69,7 +69,7 @@
 
 
 @contextlib.contextmanager
-def open_with_default(filename=None, filehandle=sys.stdout):
+def open_with_default(filename=None, filehandle=None):
     """
     Open a file for writing if given and close on completion.
 
@@ -88,6 +88,8 @@ def open_with_default(filename=None, filehandle=sys.stdout):
                 fh = open(filename, "w")
             close = True
     else:
+        if filehandle is None:
+            filehandle = sys.stdout
         fh = filehandle
 
     try: