Fixes #1372 - catch pending play request exceptions

Created by: davemevans

I have tested this in Chrome (where it seems to fix the issue) and Firefox (where it is, correctly, ignored because play does not return a Promise).

It would be good if someone can test this in Edge, IE11 and Safari.

This is probably a sticking plaster - we should possibly consider refactoring all the play/pause/load operations so this exception is not thrown.

(Note: The commit message is strictly incorrect as the catch is not silent - a log message is printed)