[FIX] web: read_group RPC

Example of failing request:
```
rpc.query({
    model: 'link.tracker.click',
    method: 'read_group',
    args: [[links_domain, ['create_date', '>', interval]], ['country_id']],
    kwargs: {groupby:'country_id'},
});
```

The RPC request built contains the following:
```
args: [[["link_id", "=", 1]], ["create_date"]]
kwargs: {groupby: "create_date:day", domain: [], fields: []}
```

This will be interpreted server side as:
```
model.read_group([['link_id', '=', 1]], ['create_date'], groupby=['create_date:day'], domain=[], fields=[])
```

2 arguments match `domain` and `fields`, which causes a crash.

opw-781300

addons/web/static/src/js/core/rpc.js

@@ -51,9 +51,15 @@ return {
         }
 
         if (options.method === 'read_group') {
-            params.kwargs.domain = options.domain || params.domain || params.kwargs.domain || [];
-            params.kwargs.fields = options.fields || params.fields || params.kwargs.fields || [];
-            params.kwargs.groupby = options.groupBy || params.groupBy || params.kwargs.groupby || [];
+            if (!(params.args && params.args[0] !== undefined)) {
+                params.kwargs.domain = options.domain || params.domain || params.kwargs.domain || [];
+            }
+            if (!(params.args && params.args[1] !== undefined)) {
+                params.kwargs.fields = options.fields || params.fields || params.kwargs.fields || [];
+            }
+            if (!(params.args && params.args[2] !== undefined)) {
+                params.kwargs.groupby = options.groupBy || params.groupBy || params.kwargs.groupby || [];
+            }
             params.kwargs.offset = options.offset || params.offset || params.kwargs.offset;
             params.kwargs.limit = options.limit || params.limit || params.kwargs.limit;
             // In kwargs, we look for "orderby" rather than "orderBy" (note the absence of capital B),

addons/web/static/tests/core/rpc_tests.js

@@ -243,6 +243,47 @@ QUnit.module('core', {}, function () {
         assert.deepEqual(query.params.kwargs.lazy, undefined, "should not enforce a default value for lazy");
     });
 
+    QUnit.test('read_group with args and kwargs', function (assert) {
+        assert.expect(9);
+        var query = rpc.buildQuery({
+            model: 'partner',
+            method: 'read_group',
+            kwargs: {
+                domain: ['name', '=', 'saucisse'],
+                fields: ['category_id'],
+                groupby: ['country_id'],
+            },
+        });
+
+        assert.deepEqual(query.params.kwargs.domain, ['name', '=', 'saucisse'], "should have ['name', '=', 'saucisse'] category_id as default domain");
+        assert.deepEqual(query.params.kwargs.fields, ['category_id'], "should have category_id as default fields");
+        assert.deepEqual(query.params.kwargs.groupby, ['country_id'], "should have country_id as default groupby");
+
+        var query = rpc.buildQuery({
+            model: 'partner',
+            method: 'read_group',
+            args: [['name', '=', 'saucisse']],
+            kwargs: {
+                fields: ['category_id'],
+                groupby: ['country_id'],
+            },
+        });
+
+        assert.deepEqual(query.params.kwargs.domain, undefined, "should not enforce a default value for domain");
+        assert.deepEqual(query.params.kwargs.fields, ['category_id'], "should have category_id as default fields");
+        assert.deepEqual(query.params.kwargs.groupby, ['country_id'], "should have country_id as default groupby");
+
+        var query = rpc.buildQuery({
+            model: 'partner',
+            method: 'read_group',
+            args: [['name', '=', 'saucisse'], ['category_id'], ['country_id']],
+        });
+
+        assert.deepEqual(query.params.kwargs.domain, undefined, "should not enforce a default value for domain");
+        assert.deepEqual(query.params.kwargs.fields, undefined, "should not enforce a default value for  fields");
+        assert.deepEqual(query.params.kwargs.groupby, undefined, "should not enforce a default value for  groupby");
+    });
+
     QUnit.test('search_read with no domain, nor fields', function (assert) {
         assert.expect(5);
         var query = rpc.buildQuery({