Test if anchor has href attribute before converting it

It is valid HTML to have anchor without href attribute.

Closes #12134
(grafted from f3a2d9b2258d6004fffc5431136bd36b010b7f9b)

--HG--
branch : 6.0

modules/marketing_automation/marketing_automation.py

@@ -567,7 +567,7 @@ class Activity(ModelSQL, ModelView):
             for kind, data, pos in stream:
                 if kind is START:
                     tag, attrs = data
-                    if tag == 'a':
+                    if tag == 'a' and attrs.get('href'):
                         href = attrs.get('href')
                         attrs -= 'href'
                         if href.startswith('unsubscribe'):

modules/marketing_email/marketing.py

@@ -425,7 +425,7 @@ class Message(Workflow, ModelSQL, ModelView):
                 for kind, data, pos in stream:
                     if kind is START:
                         tag, attrs = data
-                        if tag == 'a':
+                        if tag == 'a' and attrs.get('href'):
                             href = attrs.get('href')
                             attrs -= 'href'
                             href = short(href, str(message))