fix spurious compiler warning with -Wformat-truncation

Author: lge

checktxt.c

@@ -33,7 +33,7 @@
 
 #define xxprintf(...) \
 	{ char buffer; /* needed for older glibc */	\
-	int t = snprintf(&buffer, 1, ##__VA_ARGS__);	\
+	int t = snprintf(&buffer, 0, ##__VA_ARGS__);	\
 	elements[elidx]=alloca(t+1);			\
 	snprintf(elements[elidx], t+1, ##__VA_ARGS__);	\
 	len+=t; elidx++; }