added tracker nil check

lib/redmine_qbo/patches/issues_controller_patch.rb

@@ -24,6 +24,11 @@ module RedmineQbo
             context[:controller].flash[:error] = I18n.t(:notice_error_project_nil) + context[:issue].project.to_s
           end
 
+          if context[:issue].tracker.nil?
+            context[:issue].tracker = trackers_for_select(context[:issue]).first
+            context[:controller].flash[:error] = I18n.t(:notice_error_tracker_nil) + context[:issue].tracker.to_s
+          end
+
           return context
         end