Fix ValueError exception on empty Korean text.

[b1uec0in]

Description

Fixed check_spaces method to return a generator of length 0 instead of 1 on empty string.

This fixes the following error issue.

File ".../spacy/lang/ko/init.py", line 72, in __call__
doc = Doc(self.vocab, words=surfaces, spaces=list(check_spaces(text, surfaces)))
File "doc.pyx", line 209, in spacy.tokens.doc.Doc.__init__
ValueError: [E027] Arguments 'words' and 'spaces' should be sequences of the same length, or 'spaces' should be left default at None. spaces should be a sequence of booleans, with True meaning that the word owns a ' ' character following it.

Types of change

Bug fix

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[ines]

Thanks a lot! 👍