Don't try to parse non-existing configuration file

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D5246

tools/ade

@@ -483,6 +483,8 @@ class SysrootManager:
     def _get_url(self, version):
         url = self.url
         if not url:
+            if not self.config:
+                raise SysrootManagerError("No URL given to retrieve {0} sysroot" .format(version.distro))
             try:
                 parser = configparser.ConfigParser(interpolation=None)
                 parser.read(self.config)