Quality: Fix warning error when exporting theme

[t-hamano]

I discovered this while investigating issue #612.

c6db5435c8ed263e31927ac5468c8232.mp4

I don't know the exact cause, but it seems that this problem can be solved by adding an exit; to the end of the callback function.

The exit; also exists in the core export function.

Testing Instructions

• Add define( 'WP_DEBUG_LOG', true ); to the wp-config.php.
• Confirm that no PHP errors are logged when you export the theme.

[t-hamano]

This is a minor refactoring. With this change, we no longer check if the browser is IE, but this should not be a problem since WordPress itself does not support IE.

[pbking]

I was actually unfamiliar with msSaveBlob until looking into this change. Likewise WordPress' implementation of the anchor downloading technique so I'm happy to replace that. It works as expected.

Thank's for cleaning that up.

[pbking]

I don't know the exact cause, but it seems that this problem can be solved by adding an exit; to the end of the callback function.

Yes, I believe that in other "export" logic we have had in CBT we likewise called exit for that reason. It seems that wasn't carried over back when that transitioned to the logic we have now.

Thank you for cleaning that up.