Add coalesce option to avatar and header convert processor (#4552)

Resolve #3199

app/models/concerns/account_avatar.rb

@@ -8,7 +8,7 @@ module AccountAvatar
   class_methods do
     def avatar_styles(file)
       styles = { original: '120x120#' }
-      styles[:static] = { format: 'png' } if file.content_type == 'image/gif'
+      styles[:static] = { format: 'png', convert_options: '-coalesce' } if file.content_type == 'image/gif'
       styles
     end
 

app/models/concerns/account_header.rb

@@ -8,7 +8,7 @@ module AccountHeader
   class_methods do
     def header_styles(file)
       styles = { original: '700x335#' }
-      styles[:static] = { format: 'png' } if file.content_type == 'image/gif'
+      styles[:static] = { format: 'png', convert_options: '-coalesce' } if file.content_type == 'image/gif'
       styles
     end