fix bug in MedicalImageProperties
fix bug in MedicalImageProperties

An iterator returned from a container .find(...)
was being dereferenced without checking for a
returned end of container failure case.  The
fix checks for end of container condition before
derefencing the iterator.

Change-Id: Iccc5a31629d09a143e3712ba9c936528ef868afc

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