Stricter checks for netname and node names.

- Node names should not be empty.
- Net names should not contain slashes or start with a dot, because they are
  used in pathnames.

src/protocol.c

@@ -56,6 +56,9 @@ static char (*request_name[]) = {
 static splay_tree_t *past_request_tree;
 
 bool check_id(const char *id) {
+	if(!id || !*id)
+		return false;
+
 	for(; *id; id++)
 		if(!isalnum(*id) && *id != '_')
 			return false;