gla11y: allow python 2.6 when lxml is available

python2.6's internal xml parser is not enough for gla11y, but it can run
python-lxml fine.

Change-Id: I725471729c8e2f25ce60f1d92e08d87a96e171a5
Reviewed-on: https://gerrit.libreoffice.org/50686Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

bin/gla11y

@@ -35,12 +35,11 @@ try:
     import lxml.etree as ET
     lxml = True
 except ImportError:
+    if sys.version_info < (2,7):
+        exit()
     import xml.etree.ElementTree as ET
     lxml = False
 
-if sys.version_info < (2,7):
-    exit()
-
 progname = os.path.basename(sys.argv[0])
 suppressions = {}
 gen_suppr = None