Fixed bug where an empty vector was being accessed.
Fixed bug where an empty vector was being accessed.

The code did not properly check if a vector (idMaps) was empty
before accessing it. Fixed.

Change-Id: Id8724b2f8c47ddbb5e8178523c5b7d72c9eb4914

candy7393/VTK,keithroe/vtkoptix,keithroe/vtkoptix,mspark93/VTK,sankhesh/VTK,candy7393/VTK,mspark93/VTK,sumedhasingla/VTK,gram526/VTK,jmerkow/VTK,demarle/VTK,hendradarwin/VTK,SimVascular/VTK,msmolens/VTK,gram526/VTK,johnkit/vtk-dev,ashray/VTK-EVM,sumedhasingla/VTK,sankhesh/VTK,johnkit/vtk-dev,SimVascular/VTK,keithroe/vtkoptix,msmolens/VTK,johnkit/vtk-dev,keithroe/vtkoptix,msmolens/VTK,gram526/VTK,gram526/VTK,msmolens/VTK,berendkleinhaneveld/VTK,johnkit/vtk-dev,keithroe/vtkoptix,candy7393/VTK,ashray/VTK-EVM,hendradarwin/VTK,mspark93/VTK,msmolens/VTK,candy7393/VTK,johnkit/vtk-dev,hendradarwin/VTK,candy7393/VTK,ashray/VTK-EVM,mspark93/VTK,jmerkow/VTK,demarle/VTK,SimVascular/VTK,jmerkow/VTK,jmerkow/VTK,keithroe/vtkoptix,sankhesh/VTK,mspark93/VTK,sankhesh/VTK,msmolens/VTK,ashray/VTK-EVM,demarle/VTK,ashray/VTK-EVM,demarle/VTK,jmerkow/VTK,berendkleinhaneveld/VTK,gram526/VTK,sumedhasingla/VTK,sankhesh/VTK,SimVascular/VTK,jmerkow/VTK,gram526/VTK,SimVascular/VTK,hendradarwin/VTK,sumedhasingla/VTK,demarle/VTK,SimVascular/VTK,johnkit/vtk-dev,sankhesh/VTK,ashray/VTK-EVM,keithroe/vtkoptix,jmerkow/VTK,SimVascular/VTK,berendkleinhaneveld/VTK,hendradarwin/VTK,demarle/VTK,mspark93/VTK,berendkleinhaneveld/VTK,hendradarwin/VTK,candy7393/VTK,berendkleinhaneveld/VTK,demarle/VTK,msmolens/VTK,sumedhasingla/VTK,ashray/VTK-EVM,sankhesh/VTK,johnkit/vtk-dev,ashray/VTK-EVM,jmerkow/VTK,mspark93/VTK,gram526/VTK,berendkleinhaneveld/VTK,sumedhasingla/VTK,sumedhasingla/VTK,sankhesh/VTK,gram526/VTK,keithroe/vtkoptix,mspark93/VTK,berendkleinhaneveld/VTK,sumedhasingla/VTK,candy7393/VTK,demarle/VTK,hendradarwin/VTK,SimVascular/VTK,candy7393/VTK,msmolens/VTK