r.to.vect: -v and -b flags are mutually exclusive, disable -v flag as for other cases

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@68720 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.to.vect/main.c

@@ -141,6 +141,11 @@ int main(int argc, char *argv[])
 	    G_warning(_("Raster is not CELL, '-v' flag ignored, raster values will be lost."));
 	value_flag = 0;
     }
+    if (value_flag && no_topol->answer) {
+	G_warning(_("Vector topology is required for raster values as categories,"
+	            " '-v' flag ignored, raster values will be lost."));
+	value_flag = 0;
+    }
 
     if (!value_flag && notab_flag) {
 	G_warning(_("Categories will be unique sequence, raster values will be lost."));