Update downloader_utils.dart

[AmolPardeshi99]

"flutter 'VoidCallback' not found. final VoidCallback onDone" getting this error because the dart:ui package has not been introduced. Add the following code to the downloader_utils.dart file and it will run successfully.

Issue has been raised many times by users - https://github.com/Crdzbird/flowder/issues/9

[voldyman]

Initially i didn't want to have multiple tabs in the editor so i didn't implement it, but since there is a lot of interest for it i just might implement that. Thanks for your feedback!

[danieliser]

@voldyman - Not a problem. love what you have done so far.

[ghost]

Opening a file in an existing editor window replaces the note that is already open, instead of opening a new window, or a tab. I was expecting another window to open instead of replace the contents of the existing window. I am piggy backing off this bug report, because it feels related, but I am happy to open a new bug report as well.

[danieliser]

@christianpage Your spot on, worse yet it doesn't ask to save the previous file first so changes are lost in the process.