Fall back to URL for image alt text

If an attacment image has no description, use the URL for the
alt text instead. Having no description was causing image links
not to appear in Lynx.

resources/views/status_content.blade.php

@@ -12,7 +12,11 @@
                 >
                     <img
                         src="{{ $attachment['preview_url'] }}"
-                        alt="{{ $attachment['description'] }}"
+                        alt="{{ 
+                            $attachment['description'] === null
+                                ? $attachment['url']
+                                : $attachment['description'] 
+                        }}"
                     />
                 </a>
             </figure>