[zendframework/zf2#4624] Fix notice
[zendframework/zf2#4624] Fix notice

- Factory embedded in ViewHelperManagerFactory was not checking if
  services and/or array keys existed prior to accessing them.

turrsis/zend-mvc,svycka/zend-mvc,ezimuel/zend-mvc,ezimuel/zend-mvc,turrsis/zend-mvc,svycka/zend-mvc,MadCat34/zend-mvc,MadCat34/zend-mvc