check if type is actually a structure on field access and generate a proper error instead of a NPE
check if type is actually a structure on field access and generate a proper error instead of a NPE

git-svn-id: 6ee47c8665bf46900d9baa0afb711c5b4a0eafac@5548 e2bb083e-7f23-0410-b3a8-8253ac9ef6d8

ya7lelkom/swift-k,ya7lelkom/swift-k,swift-lang/swift-k,ya7lelkom/swift-k,swift-lang/swift-k,swift-lang/swift-k,swift-lang/swift-k,swift-lang/swift-k,swift-lang/swift-k,swift-lang/swift-k,swift-lang/swift-k,ya7lelkom/swift-k,ya7lelkom/swift-k,ya7lelkom/swift-k,swift-lang/swift-k,ya7lelkom/swift-k,swift-lang/swift-k,ya7lelkom/swift-k,ya7lelkom/swift-k,ya7lelkom/swift-k