Fix auto-filled object names enabling upload button

Affect Swift object storage file upload in Horizon.

This fix ensures that the user no longer needs to manually type
into the Object Name field to prompt the Upload button to become
enabled when the Object Name field has been automatically filled
with the name of the chosen file.

Change-Id: I11ea55cdf3aa6d0754d9e31510ff004bfa914bc1
Closes-Bug: 1348404
Merge "Fix auto-filled object names enabling upload button"