Fixed null dereference when null passed as attribute list to eglCreateContext.
Fixed null dereference when null passed as attribute list to eglCreateContext.

I tested that the samples still work and that they fail as expected, but do not crash, if the attribute list argument is null.

Review URL: http://codereview.appspot.com/2725042

csulmone/angle,csulmone/angle,csulmone/angle,csulmone/angle