Fixes issue when pageX / pageY are undefined ( found it w/ Mobile Safari )

[tsanko]

... more cases may exist.

May be related to #173.

[clemfernandez]

This needs to be merged, I experienced the same problem after reading many times that ngDraggable was the directive to use with Ionic Framework. With this fix, it really is !

[callado4]

I experienced this bug on both Chrome on Android/iPhone and Mobile Safari. If it helps to reproduce, it happened within a bootstrap row, but I can't say for sure if that was the root cause (the examples did work on my devices).

This fix worked for me so I'm using itin for my project.

[hylke45]

Thank you, this works for me with a complicated Ionic app with bootstrap. (saved me just in time for meeting)