Fix options.reset handling

[mbrgm]

First, I removed the obsolete if condition surrounding the if..else block.

Then, when options.reset is true, the expected behavior is to reset the property value to the begin value, which works. But when options.reset is false or undefined, the property value would be set to false or undefined at the end of the animation, which is not the desired effect. I fixed this to reflect the expected behavior.

[brentvatne]

Thanks! I'll get this into the next release, I'm going to add some support for animating the backdrop and modal separately in it