Fix initialized check in Sentry::Rails::CaptureExceptions

Author: sl0thentr0py

sentry-rails/lib/sentry/rails/capture_exceptions.rb

@@ -27,6 +27,7 @@ def transaction_op
 
       def capture_exception(exception, env)
         # the exception will be swallowed by ShowExceptions middleware
+        return unless Sentry.initialized?
         return if show_exceptions?(exception, env) && !Sentry.configuration.rails.report_rescued_exceptions
 
         Sentry::Rails.capture_exception(exception).tap do |event|