fixed bug in MnistImageFile::numEntries()
fixed bug in MnistImageFile::numEntries()

Change-Id: Ib3d45d8555cfab3f511bbfe55ecf1a5e1de66b0a

csail-csg/connectal,cambridgehackers/connectal,8l/connectal,hanw/connectal,csail-csg/connectal,8l/connectal,8l/connectal,hanw/connectal,hanw/connectal,8l/connectal,hanw/connectal,cambridgehackers/connectal,hanw/connectal,cambridgehackers/connectal,csail-csg/connectal,chenm001/connectal,chenm001/connectal,cambridgehackers/connectal,csail-csg/connectal,chenm001/connectal,cambridgehackers/connectal,csail-csg/connectal,chenm001/connectal,chenm001/connectal,8l/connectal