STYLE: use nullptr instead of 0 in autoPtr, tmp etc.

...b/functionObjects/functionObjectList/functionObjectList.C

src/OpenFOAM/memory/Xfer/Xfer.H

src/OpenFOAM/memory/Xfer/XferI.H

src/OpenFOAM/memory/autoPtr/autoPtr.H

src/OpenFOAM/memory/autoPtr/autoPtrI.H

src/OpenFOAM/memory/tmp/tmp.H

src/OpenFOAM/memory/tmp/tmpI.H

src/OpenFOAM/memory/tmpNrc/tmpNrc.H

src/OpenFOAM/memory/tmpNrc/tmpNrcI.H