Added a fix for an intermittent IE issue

Internet Explorer 10 (on Windows 7 inside a VM) would sometimes report that `this.layout.size` was null or undefined when running `layoutPosition()` for the first item in my Masonry layout.  I could never discern any pattern as to when IE decided to issue the error and when it didn't, leads me to think there may be a race condition somewhere in Outlayer.  Being more intimately familiar with Outlayer's inner workings, you probably have a better idea of what's going on than I do.  At any rate, this fix appears to have corrected the issue for me, and I wanted to share it.