Coverity check on master@bd16929, CID 71489: Uninitialized pointer field (UNINIT_CTOR).

DialogBase class member m_fontChooser, m_pStylePage and m_pageItem has not been
initialised in the constructor. Also prevent zero pointer access to m_fontChooser
and m_pStylePage caused by code design issues. Remove obsolate, not initialised
m_pStylePage class members in derived classes.

CCBUG:340646