apply: avoid possible bogus pointer

When parsing "index" lines from a git-diff, we look for a
space followed by the mode. If we don't have a space, then
we set our pointer to the end-of-line. However, we don't
double-check that our end-of-line pointer is valid (e.g., if
we got a truncated diff input), which could lead to some
wrap-around pointer arithmetic.

In most cases this would probably get caught by our "40 <
len" check later in the function, but to be on the safe
side, let's just use strchrnul to treat end-of-string the
same as end-of-line.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -1073,7 +1073,7 @@ static int gitdiff_index(const char *line, struct patch *patch)
 
 	line = ptr + 2;
 	ptr = strchr(line, ' ');
-	eol = strchr(line, '\n');
+	eol = strchrnul(line, '\n');
 
 	if (!ptr || eol < ptr)
 		ptr = eol;