fix a bug that makes that URLSave always fails

Author: mmatera

mathics/builtin/files_io/filesystem.py

@@ -2274,7 +2274,7 @@ def apply_2(self, url, filename, evaluation, **options):
         url = url.value
         if filename is None:
             result = urlsave_tmp(url, None, **options)
-        elif filename.get_head_name() == "String":
+        elif isinstance(filename, String):
             filename = filename.value
             result = urlsave_tmp(url, filename, **options)
         else:

mathics/core/streams.py

@@ -43,9 +43,10 @@ def urlsave_tmp(url, location=None, **kwargs):
             with open(location, "wb") as fp:
                 fp.write(r.content)
                 result = fp.name
+            return result
         except Exception:
-            result = None
-    return result
+            return None
+    return None
 
 
 def path_search(filename: str) -> Tuple[str, bool]: