Remove isset() check in Sanitizer::setupAttributeWhitelist()

Declared variables have a default value of null, so there is
no point to use isset() to check only if it has the value null.

Also changed the location of the line break to group variable
declarations.

Change-Id: Ic36fc95db86909d8b5075954a72afa479fa20d0d
Merge "Remove isset() check in Sanitizer::setupAttributeWhitelist()"