message: Safer casting in ClangExpressionParser code completion
  Summary:
  Makes the code a bit safer in the unlikely situation that we don't get a ClangUserExpression
  when doing code completion.
  Reviewers: aprantl, jingham
  Subscribers: labath, jdoerfert, lldb-commits
  Tags: #lldb
diff: @@ -857,8 +857,8 @@ bool ClangExpressionParser::Complete(CompletionRequest &request, unsigned line,
  // To actually get the raw user input here, we have to cast our expression to
  // the LLVMUserExpression which exposes the right API. This should never fail
  // as we always have a ClangUserExpression whenever we call this.
  - LLVMUserExpression &llvm_expr = *static_cast<LLVMUserExpression *>(&m_expr);
  - CodeComplete CC(request, m_compiler->getLangOpts(), llvm_expr.GetUserText(),
  + ClangUserExpression *llvm_expr = cast<ClangUserExpression>(&m_expr);
  + CodeComplete CC(request, m_compiler->getLangOpts(), llvm_expr->GetUserText(),
  typed_pos);
  // We don't need a code generator for parsing.
  m_code_generator.reset();
  