Use get method in Binary widget when field has not get_data method

The binary widget can be used with non-binary field which does not have
get_data method like Char.

issue5989
review29701002

src/view/form.js

@@ -2936,7 +2936,13 @@
             var mimetype = params.mimetype || 'application/octet-binary';
             var field = this.field();
             var record = this.record();
-            field.get_data(record).done(function(data) {
+            var prm;
+            if (field.get_data) {
+                prm = field.get_data(record);
+            } else {
+                prm = jQuery.when(field.get(record));
+            }
+            prm.done(function(data) {
                 var blob = new Blob([data], {type: mimetype});
                 var blob_url = window.URL.createObjectURL(blob);
                 if (this.blob_url) {