Fixed array underrun caught by clang ubsan

It complained:
vtkOOGLExporter.cxx:228:3: runtime error: index -4 out of bounds for type 'char [256]'

Seems to be an imbalance of VTK_INDENT macro usage.

Change-Id: Ie19ecf64cc720c4e8ea90e0abaec73b1cf7de6b3
Merge topic 'array-underrun-fix' into master

987212dc Fixed array underrun caught by clang ubsan