More issues found by static analysis

modules/ml/src/ann_mlp.cpp

@@ -1259,7 +1259,7 @@ public:
             prev_dEdw_sign[i] = Mat::zeros(weights[i].size(), CV_8S);
             dEdw[i] = Mat::zeros(weights[i].size(), CV_64F);
         }
-
+        CV_Assert(total > 0);
         int dcount0 = max_buf_size/(2*total);
         dcount0 = std::max( dcount0, 1 );
         dcount0 = std::min( dcount0, count );