Assert on low side as well
Assert on low side as well

Summary: One model was passing -1s in the label blob, causing illegal memory access when computing the label-cross entropy. Improving the assertion causes it to fail properly.

Reviewed By: prigoyal

Differential Revision: D4491848

fbshipit-source-id: 5c48e43b0a8928cac70e939d69d23c94c07511b9

bwasti/caffe2,sf-wind/caffe2,pietern/caffe2,davinwang/caffe2,Yangqing/caffe2,bwasti/caffe2,xzturn/caffe2,bwasti/caffe2,xzturn/caffe2,Yangqing/caffe2,davinwang/caffe2,davinwang/caffe2,Yangqing/caffe2,pietern/caffe2,xzturn/caffe2,pietern/caffe2,davinwang/caffe2,Yangqing/caffe2,sf-wind/caffe2,xzturn/caffe2,bwasti/caffe2,davinwang/caffe2,bwasti/caffe2,caffe2/caffe2,xzturn/caffe2,sf-wind/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2,sf-wind/caffe2,sf-wind/caffe2