swift-api-digester: Ignore the declarations that have no accessibility set. rdar://35375615 (swiftlang#12784)

Author: nkcsgexi

tools/swift-api-digester/swift-api-digester.cpp

@@ -1282,6 +1282,9 @@ static bool shouldIgnore(Decl *D) {
       return true;
     if (VD->getBaseName().empty())
       return true;
+    // This shouldn't happen, being forgiving here.
+    if (!VD->hasAccess())
+      return true;
     switch (VD->getFormalAccess()) {
     case AccessLevel::Internal:
     case AccessLevel::Private: