BUG: Uninitialized memory in GL2PSExporter

The constructor failed to initialize TextAsPath. Later the
uninitialized variable was used to set
vtkGL2PSUtilities::TextAsPath. When accessed in vtkGL2PSUtilities
valgrind triggered a "Conditional jump or move depends on
uninitialised value(s)"

Change-Id: I6548c02ae8cfb0f5ccb1abb614416248a203a8c5
Merge topic 'UninitializedMemory_vtkGL2PSExporter' into master

827c302a BUG: Uninitialized memory in GL2PSExporter