fix($compile): bind ng-attr-* even if unbound attribute follows ng-attr-*

**TEST PR** Just want to make sure this works on IE8...

Previously, <element ng-attr-foo="{{binding}}" foo="bar"></element>'s "foo"
attribute would always equal "bar", because the bound version was overwritten.
This CL corrects this behaviour and ensures that the ordering of attributes
does not have an effect on whether or not ng-attr-bound attributes do their
work.

Closes #7739