error when destroying a modal dialog

If you destroy a modal dialog before showing it the destroy function try to remove a null overlay.

I solved the problen by modifying the code and removin the overlay only if overlayInstances > 0.

_destroyOverlay: function() {

if ( !this.options.modal ) {

return;

}

if ( $.ui.dialog.overlayInstances > 0 ) {

$.ui.dialog.overlayInstances--;

if ( !$.ui.dialog.overlayInstances ) {

this._off( this.document, "focusin" );

}

this.overlay.remove();

}

}

sample in http://jsfiddle.net/JMGrange/QUT5m/