Prevent crash in vtkPVContextView::GetFormattedTitle()

Add a guard against initializing the title from a null title string.
15 jobs for 19409-parallel-coords-crash
Status Name Job ID Coverage
  External
passed cdash

passed ghostflow-branch-check-master

failed paraview@master-dres-osx-shared-release+gui+python2

failed paraview@master-luigi-linux-shared-release+gui+mpi+python2

pending paraview@master-nemesis-windows-shared-release+gui+kits+mpi+python2
pending paraview@master-nemesis-windows-shared-release+gui+mpi
passed paraview@master-taanab-linux-shared-release+adios2+mpi+python2

failed paraview@master-taanab-linux-static-release+adios2+mpi+offscreen+osmesa+python2

00:04:02

pending paraview@master-tylo-windows-shared-release+gui+python3+qtmin+tbb
pending paraview@master-tylo-windows-shared-release+gui+python3+tbb
failed paraview@master-vall-linux-shared-debug+adios2+doc+extdeps+gui+mpi+python3

failed paraview@master-dres-osx-shared-release+gui+python2

00:50:21

failed paraview@master-luigi-linux-shared-release+gui+mpi+python2

00:49:48

passed paraview@master-taanab-linux-shared-release+adios2+mpi+python2

00:03:10

failed paraview@master-vall-linux-shared-debug+adios2+doc+extdeps+gui+mpi+python3

01:15:42