Fixes NullReferenceException in GeneratorRewriter when creating a generator for lambda with assingment to static fields.
Fixes NullReferenceException in GeneratorRewriter when creating a generator for lambda with assingment to static fields.

(Shelveset: GeneratorFix;REDMOND\igorzi | SNAP CheckinId: 10811)

TFS Changeset 1824266

IronLanguages/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,IronLanguages/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,slozier/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,slozier/ironpython2