Merge branch '5730-php-error-htmlentities-expects-parameter-1-to-be-string-array-given-usr-share-fusiondirectory-include-simpleplugin-class_attribute-inc-line-563' into '1.3-dev'

Resolve "PHP error: htmlentities() expects parameter 1 to be string, array given (/usr/share/fusiondirectory/include/simpleplugin/class_Attribute.inc, line 563)"

See merge request fusiondirectory/fd!72

(cherry picked from commit 87ca56dd)

054d5f34 🚑 fix(simpleplugin): Fix PHP error in readonly mode