check for 0 length string in strip_trailing_slash

size_t is unsigned, so if strlen returned 0, path[end] would try to
access something unexpected

main.c

@@ -308,7 +308,10 @@ cgi(const char *cgicmd)
 void
 strip_trailing_slash(char *path)
 {
-	size_t end = strlen(path) - 1;
+	size_t end = strlen(path);
+	if (end == 0)
+		return;
+	end--;
 	while (path[end] == '/')
 		path[end--] = '\0';
 }