fix: handle active storage preview error for password protected pdfs (#11888)

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/controllers/slack_uploads_controller.rb

@@ -17,7 +17,12 @@ class SlackUploadsController < ApplicationController
   end
 
   def blob_url
-    url_for(@blob.representation(resize_to_fill: [250, nil]))
+    # Only generate representations for images
+    if @blob.content_type.start_with?('image/')
+      url_for(@blob.representation(resize_to_fill: [250, nil]))
+    else
+      url_for(@blob)
+    end
   end
 
   def avatar_url

app/models/attachment.rb

@@ -60,11 +60,9 @@ class Attachment < ApplicationRecord
   end
 
   def thumb_url
-    if file.attached? && file.representable?
-      url_for(file.representation(resize_to_fill: [250, nil]))
-    else
-      ''
-    end
+    return '' unless file.attached? && image?
+
+    url_for(file.representation(resize_to_fill: [250, nil]))
   end
 
   def with_attached_file?