Parse only init_debug option with non-empty argument.

Matching empty string makes rm_so and rm_eo of struct regmatch_t have
the same value, in this case both of them are 11. This causes a call to
atoi("\0") whose return value 0 is just the initial value of 'debug'.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

debug.c

@@ -36,7 +36,7 @@ void debug_init(void)
 	line[r] = '\0';
 	close(fd);
 
-	regcomp(&pat_cmdline, "init_debug=([0-9]*)", REG_EXTENDED);
+	regcomp(&pat_cmdline, "init_debug=([0-9]+)", REG_EXTENDED);
 	if (!regexec(&pat_cmdline, line, 2, matches, 0)) {
 		line[matches[1].rm_eo] = '\0';
 		debug = atoi(&line[matches[1].rm_so]);