added else-block for if-block on line #699

[srcoulombe]

Added missing else-block for the if-block if norm != "NONE": on line #699. Added else-block sets c1Norm and c2Norm to None.

Calls to c1Norm and c2Norm include those in:

• normalizematrix.__init__ (which sets c1Norm and c2Norm as instance parameters)
• normalizematrix.getDataFromBinRegion (which passed c1Norm and c2Norm as arguments to multiprocessed calls to readBlockWorker)
• readBlockWorker (which only uses c1Norm and c2Norm in an if-block: if norm != "NONE")

This would resolve https://github.com/aidenlab/straw/issues/45