fix(social): add image dimensions and alt text to Open Graph tags

- Add og:image:width (1200) and og:image:height (630) for proper preview
- Add og:image:alt for accessibility
- Fix nil error when workshop has no host

Author: mroderick

app/views/shared/_meta_tags.html.haml

@@ -2,6 +2,9 @@
 %meta{ property: 'og:type', content: 'website' }
 %meta{ property: 'og:url', content: request.original_url }
 %meta{ property: 'og:image', content: image_url('codebar-social.jpg') }
+%meta{ property: 'og:image:width', content: '1200' }
+%meta{ property: 'og:image:height', content: '630' }
+%meta{ property: 'og:image:alt', content: 'codebar - making tech more diverse and welcoming' }
 %meta{ property: 'og:description', content: 'Making tech more diverse and welcoming by bringing people together and helping teach programming skills.' }
 %meta{ property: 'og:site_name', content: 'codebar' }
 %meta{ property: 'og:locale', content: 'en_GB' }

app/views/workshops/_meta_tags.html.haml

@@ -2,7 +2,7 @@
   title = if workshop.virtual?
     t('workshops.virtual.title_with_date', chapter: workshop.chapter.name, date: humanize_date(workshop.date_and_time))
   else
-    t('workshop.title', host: workshop.host.name, date: humanize_date(workshop.date_and_time))
+    t('workshop.title', host: workshop.host&.name || 'codebar', date: humanize_date(workshop.date_and_time))
   end
   url = request.original_url
   image = workshop.host.try(:image_url).presence || image_url('codebar-social.jpg')