fixed, when datepicker opens incorrectly, when page doesn't have scroll

[VadymMakhonin]

#643

[ZeStrid3r]

Hi, this doesn't fix the (re)position issue #643:

show: function()
          {
              if (!this.isVisible()) {
 -               removeClass(this.el, 'is-hidden');
                  this._v = true;
                  this.draw();
                  if (this._o.bound) {
                      addEvent(document, 'click', this._onClick);
                      this.adjustPosition();
                  }
 +               removeClass(this.el, 'is-hidden');
                  if (typeof this._o.onOpen === 'function') {
                      this._o.onOpen.call(this);
                  }

adjustPosition function cannot read offsetHeight value if element has class "is-hidden", remove class function need to be placed after draw function AND before adjustPosition function:

show: function()
          {
              if (!this.isVisible()) {
 -               removeClass(this.el, 'is-hidden');
                  this._v = true;
                  this.draw();
 +               removeClass(this.el, 'is-hidden');
                  if (this._o.bound) {
                      addEvent(document, 'click', this._onClick);
                      this.adjustPosition();
                  }
                  if (typeof this._o.onOpen === 'function') {
                      this._o.onOpen.call(this);
                  }

[rikkert]

Good catch, can you please make a PR for this?