Textarea: readEditor(): call callback after editing

[plepe]

I noticed, that the readEditor() callback on the Textarea widget won't be called after closing the external editor. This little change fixes this problem.

[GottZ]

after looking at the whole file i suggest adding a return statement in front of that callback call. return callback(null, value);

[plepe]

Does not really change anything, but yes - why not. I modified the commit and force-pushed the change.