Fix #13700, consistently use the original name in error message

IPython/utils/path.py

@@ -83,12 +83,13 b' def get_py_filename(name):'
     """
 
     name = os.path.expanduser(name)
-    if not os.path.isfile(name) and not name.endswith('.py'):
-        name += '.py'
     if os.path.isfile(name):
         return name
-    else:
-        raise IOError('File `%r` not found.' % name)
+    if not name.endswith('.py'):
+        py_name = name + '.py'
+        if os.path.isfile(py_name):
+            return py_name
+    raise IOError('File `%r` not found.' % name)
 
 
 def filefind(filename: str, path_dirs=None) -> str: