`_elems()` with mods doesn't work

[belozer]

Test case

it('should use difference caches for elem mods', function() {
    var Block = bemDom.declBlock('block');
    rootNode = createDomNode({
        block : 'block',
        content : [
            { elem : 'elem', elemMods : { m1 : true } },
            { elem : 'elem', elemMods : { m2 : true } },
            { elem : 'elem', elemMods : { m2 : true } },
            { elem : 'elem' },
        ]
    });

    block = rootNode.bem(Block);

    // Expected: 1, Actual: 1
    block._elems({ elem : 'elem', modName : 'm1' }).size().should.be.equal(1);

    // Expected: 2, Actual: 1
    block._elems({ elem : 'elem', modName : 'm2' }).size().should.be.equal(2);

    // Expected: 4, Actual: 1
    block._elems('elem').size().should.be.equal(4);
});

CodePen https://codepen.io/belozer/pen/eLYVPK?editors=0012