[NNotepad] Fix #253 e.target.close is not a function error

[ibelem]

Fix #253

Click "Close" button in "Show generated code" or "Show documentation" dialog not only triggers button click event but also the dialog click event, which makes the e.target in dialog click event quals the dialog element and button element, but there is no close() method for buttons.

@inexorabletash @anssiko @Honry PTAL

[Honry]

LGTM, thanks!

[inexorabletash]

This is fine, but I think you could also do if (e.target !== dialog) return;

Sorry about this - obviously I added the "click outside to close" later and didn't test that the buttons still worked.

[ibelem]

Thanks @inexorabletash , if (e.target !== dialog) return; is much more concise and precise, PTAL.

[inexorabletash]

LGTM thanks!