BUG/MEDIUM: tools: off-by-one in quote_arg()

This function may write the \0 one char too far in the static array.
There is no effect right now as the function has never been used except
maybe in code that was never released. Out-of-tree code might possibly
be affected though (hence the MEDIUM flag).

No backport is needed.

Reported-by: Dinko Korunic <dkorunic@reflected.net>

src/standard.c

@@ -1567,7 +1567,7 @@ const char *quote_arg(const char *ptr)
 	if (!ptr || !*ptr)
 		return "end of line";
 	val[0] = '\'';
-	for (i = 1; i < sizeof(val) - 1 && *ptr; i++)
+	for (i = 1; i < sizeof(val) - 2 && *ptr; i++)
 		val[i] = *ptr++;
 	val[i++] = '\'';
 	val[i] = '\0';