message: Handle errors in SwiftASTContext
diff: @@ -3204,8 +3204,10 @@ public:
  SymbolFile *sym_file = m_swift_ast_ctx.GetSymbolFile();
  if (!sym_file)
  return;
  - auto *clang_ctx = llvm::dyn_cast_or_null<ClangASTContext>(
  - sym_file->GetTypeSystemForLanguage(eLanguageTypeObjC));
  + auto ast_ctx = sym_file->GetTypeSystemForLanguage(eLanguageTypeObjC);
  + if (!ast_ctx)
  + return llvm::consumeError(ast_ctx.takeError());
  + auto *clang_ctx = llvm::dyn_cast_or_null<ClangASTContext>(&(*ast_ctx));
  if (!clang_ctx)
  return;
  clang::FileSystemOptions file_system_options;
  @@ -3226,11 +3228,15 @@ public:
  continue;
  clang::ASTImporter importer(to_ctx, file_manager, *from_ctx,
  file_manager, false);
  - clang::QualType clang_type(
  + llvm::Expected<clang::QualType> clang_type(
  importer.Import(ClangUtil::GetQualType(compiler_type)));
  + if (!clang_type) {
  + llvm::consumeError(clang_type.takeError());
  + continue;
  + }
  // FIXME: Support more than structs.
  - auto *clang_record_type = clang_type->getAsStructureType();
  + auto *clang_record_type = (*clang_type)->getAsStructureType();
  if (!clang_record_type)
  continue;
  clang::Decl *clang_decl = clang_record_type->getDecl();
  