[BUGFIX] Missing closing tag in ElementBrowser

There is missing " />" at the end for $clickIcon, which refers to
the thumbnail in the element browser.
Resolves: #52546
Releases: 6.2, 6.1, 6.0
Change-Id: I2da27190db0ca627c2967750f828c6748b039356
Reviewed-on: https://review.typo3.org/24437
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe