Image upload dialog: Dialog must have a Close button instead of OK/Cancel to close the dialog after errors are shown

Scenario
1) Go to Images and choose Add Image...
2) Select an image of 10MB (too large).
3) Click OK.
Expected: Error information is shown with Close button to close the dialog
Actual: Error information is shown with Cancel button and disabled OK button.
As there is no pending action to be cancelled the dialog must have a Close button