fix for fontSize going NaN

[rcyrus]

Under chrome sometimes getComputedStyle will return "" which then causes parseInt to produce NaN.

If this happens try to get font-size out of the elmement attribute hash so dy attribute can be computed.

[hbarudin]

Bump to this - @DmitryBaranovskiy (not sure who is in charge of merging PRs for this repo). I've used an identical fix in a local version of raphael, but getting this fix into master so I can use the Bower package would be awesome.