check current_user is defined in agent_is crawler

[kosarko]

I did as suggested in #1736 (comment) to disable search tracking, ie config.crawler_detector = lambda { |req| true }, but that resulted in:

NameError in CatalogController#index
undefined local variable or method `current_user' for #<CatalogController:0x0000000000ceb8>

Did you mean?
current_or_guest_user
Extracted source (around line #76):
              
74  def agent_is_crawler?
75    crawler_proc = blacklight_config.crawler_detector
76    return false if crawler_proc.nil? || current_user.present?
77
78    crawler_proc.call(request)
79  end

Rails.root: /src/blacklightapp

Application Trace | Framework Trace | Full Trace
blacklight (7.13.2) app/controllers/concerns/blacklight/search_context.rb:76:in `agent_is_crawler?'
blacklight (7.13.2) app/controllers/concerns/blacklight/search_context.rb:41:in `find_search_session'
blacklight (7.13.2) app/controllers/concerns/blacklight/search_context.rb:32:in `current_search_session'
blacklight (7.13.2) app/controllers/concerns/blacklight/search_context.rb:37:in `set_current_search_session'
activesupport (6.1.3.2) lib/active_support/callbacks.rb:427:in `block in make_lambda'

I've installed blacklight without devise, I have no need for users logging in, yet.
The patch seems to fix the issue, it just checks something called current_user is defined...