PATCH: fix potential memory leak introduced in 5.12.0

Nicholas Clark pointed out that my patch to toke.c to fix the \N{...} 
problems had a potential memory leak.

I'm uncertain if this should go into 5.12.1, hence by definition, it 
shouldn't.  But it does fix a potential leak introduced into 5.12.0, so 
I'm submitting it in time to be considered for 5.12.1.

• PATCH: fix potential memory leak introduced in 5.12.0 by karl williamson
• Re: PATCH: fix potential memory leak introduced in 5.12.0 by Rafael Garcia-Suarez