[BUGFIX] Do not add category to empty table names

If the $GLOBALS['TYPO3_CONF_VARS']['SYS']['defaultCategorizedTables']
is empty or you have empty strings between commas then we try to add
empty tablenames to the table definitions.

This is fixed by setting removeEmptyValues to true in trimExplode
and adding a RuntimeException to the add function to prevent
others (extensions) breaking the functionality.

Resolves: #48381
Releases: 6.2, 6.1
Change-Id: I4a8d43a0ff75da298ace4f1d33a5dcf2d2ac569f
Reviewed-on: https://review.typo3.org/21394
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters