core: repair CV_Assert() messages

Multi-argument CV_Assert() is accessible via CV_Assert_N() (with malformed messages).

samples/dnn/segmentation.cpp

@@ -57,7 +57,6 @@ int main(int argc, char** argv)
     float scale = parser.get<float>("scale");
     Scalar mean = parser.get<Scalar>("mean");
     bool swapRB = parser.get<bool>("rgb");
-    CV_Assert(parser.has("width"), parser.has("height"));
     int inpWidth = parser.get<int>("width");
     int inpHeight = parser.get<int>("height");
     String model = parser.get<String>("model");
@@ -99,7 +98,13 @@ int main(int argc, char** argv)
         }
     }
 
-    CV_Assert(parser.has("model"));
+    if (!parser.check())
+    {
+        parser.printErrors();
+        return 1;
+    }
+
+    CV_Assert(!model.empty());
     //! [Read and initialize network]
     Net net = readNet(model, config, framework);
     net.setPreferableBackend(backendId);