Improve handling of missing typetag strings
Improve handling of missing typetag strings

When it's time to read the typetag string, check that the current
character is ',' first, and then attempt to read the entire string.

Signed-off-by: John Else <37b74501daa612e48fea94f9846ed4ddeb6a8f07@citrix.com>

johnelse/ocaml-osc