PHP Notice undefined string offset in post.php

[solarissmoke]

I'm getting the following PHP Notice in debug mode when creating/editing posts:

Uninitialized string offset: 0 in \wp\wp-admin\includes\post.php on line 1549

It's because some of the TinyMCE initArray options are empty strings. Suggest adding an extra check in line 1549's elseif.

Check that string is non-empty before looking for first character

(In [16112]) Check for empty strings before indexing into them. Fixes #15265 props solarissmoke.