Hi,

If multibyte support is enabled and TERM is dumb, typing double-width
characters causes segmentation fault:

ueno@localhost % LANG=en_US.utf8 TERM=dumb zsh -f
localhost% <-- type あ with some input method
*** glibc detected *** zsh: free(): invalid next size (fast): 0x00000000018dd500 ***
zsh: abort (core dumped)  LANG=en_US.utf8 TERM=dumb zsh -f

This is because zle_refresh.c:singlerefresh() does not calculate the
size of new line buffer correctly.  Here is a patch for this.