PATCH: Don't treat NUL as a combining character

[Mikael Magnusson <mikachu@gmail.com>]

As title, if you input
% something<ctrl-v ctrl-space>
while combining_chars is set, it visually doesn't appear, but toggling
the option makes it appear again (just like for actual combining
characters).

(I was momentarily confused why a command looking like *.mp4(e'fattr
notes test') worked, then i remembered my ^_e bind to enter an e::
glob uses ^@ as the separator. Normally I don't have combining_chars
set, but this directory contains some NFD files.)

I considered using L'\0' to clarify the intent, but I have no idea if
all compilers support wchar literals?

index 6b3cb97..13c053c 100644
--- i/Src/zsh.h
+++ w/Src/zsh.h
@@ -2982,9 +2982,9 @@ typedef wint_t convchar_t;
  * We can't be quite sure the wcwidth we've provided is entirely
  * in agreement with the system's, so be extra safe.
  */
-#define IS_COMBINING(wc)       (WCWIDTH(wc) == 0 && !iswcntrl(wc))
+#define IS_COMBINING(wc)       (wc != 0 && WCWIDTH(wc) == 0 && !iswcntrl(wc))
 #else
-#define IS_COMBINING(wc)       (WCWIDTH(wc) == 0)
+#define IS_COMBINING(wc)       (wc != 0 && WCWIDTH(wc) == 0)
 #endif
 /*
  * Test for the base of a combining character.


-- 
Mikael Magnusson