Update file_info.go (fix errcheck issue) (mattermost#28966)

Co-authored-by: Ben Schumacher <[email protected]>

server/.golangci.yml

@@ -92,7 +92,6 @@ issues:
         channels/app/export_test.go|\
         channels/app/file.go|\
         channels/app/file_bench_test.go|\
-        channels/app/file_info.go|\
         channels/app/file_test.go|\
         channels/app/helper_test.go|\
         channels/app/import_functions.go|\

server/channels/app/file_info.go

@@ -40,7 +40,9 @@ func getInfoForBytes(name string, data io.ReadSeeker, size int) (*model.FileInfo
 
 			if info.MimeType == "image/gif" {
 				// Just show the gif itself instead of a preview image for animated gifs
-				data.Seek(0, io.SeekStart)
+				if _, err := data.Seek(0, io.SeekStart); err != nil {
+					return info, model.NewAppError("getInfoForBytes", "app.file_info.seek.gif.app_error", nil, "", http.StatusBadRequest).Wrap(err)
+				}
 				frameCount, err := imgutils.CountGIFFrames(data)
 				if err != nil {
 					// Still return the rest of the info even though it doesn't appear to be an actual gif

server/i18n/en.json

@@ -5162,6 +5162,10 @@
     "id": "app.file_info.save.app_error",
     "translation": "Unable to save the file info."
   },
+  {
+    "id": "app.file_info.seek.gif.app_error",
+    "translation": "Unable to seek to the beginning of the GIF data."
+  },
   {
     "id": "app.file_info.set_searchable_content.app_error",
     "translation": "Unable to set the searchable content of the file."