fix  case when boundary condition flag gets improperly overwritten

This case only poses  a problem when no node flags are specified (or the DOFBoundaryConditions class is set to ignore nodal flags). As a rule we should probably force  nodal material flags on the geometry since nodes sharing facets with different flags have to be assigned arbitrarily.
Merge pull request #114 from erdc-cm/fix_DOFBoundaryMaterialFlag

fix  case when boundary condition flag gets improperly overwritten