gopher: ensure slash after entity type in links

This prevents links with null selectors being interpreted as pointing to
a (likely non-existent) file gopher://server/1
An example of a page with such links: gopher://gopher.floodgap.com/1/new

src/protocol/gopher/gopher.c

@@ -527,6 +527,10 @@ add_gopher_menu_line(struct string *buffer, unsigned char *line)
 			add_format_to_string(&address, "gopher://%s/%c",
 				host, entity);
 
+			/* Ensure we put a slash after entity type */
+			if (selector[0] != '/')
+				add_char_to_string(&address, '/');
+
 			/* Encode selector string */
 			encode_selector_string(&address, selector);
 		}