[BUGFIX] Prevent duplicating icons definition in the page tree

Additionally add a console warning when doktype doesn't have an icon

Releases: master, 8.7
Resolves: #84018
Change-Id: If220a53e1dacf4d5b4fabdfcfc25331e83fe6811
Reviewed-on: https://review.typo3.org/55904


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Tested-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>