Reset ctx.repo to NULL when the config parser is finished

This global variable is used by the config parsing callback to keep track
of the currently configured repository. If it is not reset to NULL when
the config parser is finished, and neither `url` or `r` is specified on the
querystring, cgit will wrongly consider the last configured repo as
selected.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -440,6 +440,7 @@ int main(int argc, const char **argv)
 
 	parse_configfile(cgit_config_env ? cgit_config_env : CGIT_CONFIG,
 			 config_cb);
+	ctx.repo = NULL;
 	if (getenv("SCRIPT_NAME"))
 		ctx.cfg.script_name = xstrdup(getenv("SCRIPT_NAME"));
 	if (getenv("QUERY_STRING"))