scrollToElement fails when element has position of 0

Found an issue where if you are trying to use scrollToElement with an element that is positioned at either top 0 or left 0, jscrollpane fails to scroll to that element.

Checking if a variable is undefined using a regular
'if(variable)'
is generally unsafe, especially when you're dealing with coordinates.
Since you potentially run into the issue of
variable = 0
if(variable)