Joe can't open or save a file that ends with a comma
(such a a flagless maildir file).
The editor starts as if begining a new file.
$ echo "test" >foobar,
$ joe foobar,
Editor is empty with "New File".
$ joe "foobar,"
Enter "this is a test"
Joe says "file foobar, saved".
(the , was dropped form the samed filename)