Gray out the "Select" button when uploading an image through the image modal for the second time

Marking the issue as bug because it can create an unwanted behavior for the end user. One coud argue that is more an usability improvement.

When uploading an image through the CKEditor image upload modal for the first time in an editing session, the upload flow will be as follows :

• The user clicks on the image icon in the CKEditor toolbar
• Then the user clicks on the "Upload" tab in the modal
• The "select" button of the modal is grayed out

The user has to select the file that needs to be uploaded, click on "Upload" and then click on "Select" to continue with the image.

When coming back on this modal later on in the same editing session (without refreshing the page), the field used to select the file to upload will be already pre-filled with the image previously uploaded. Because of this, the "Select" button of the modal will stay enabled when accessing the "Upload" tab.

The issue is that a user can then browse for an image on his computer, and then click directly on "Select" instead of "Upload" then "Select". If the user directly clicks on "Select" without clicking on "Upload" first, then the last uploaded image is inserted in the page.