Order tags to search by alphabetically

We were ordering one group of tags alphabetically and then adding
another group of tags which wasn't ordered alphabetically, which didn't
make much sense.

app/helpers/budgets_helper.rb

@@ -54,9 +54,10 @@ module BudgetsHelper
   end
 
   def investment_tags_select_options(budget, context)
-    tags = budget.investments.tags_on(context).order(:name).pluck(:name)
-    tags = tags.concat budget.tag_list_on(context)
-    tags.uniq
+    taggables = [budget] + budget.investments
+    Tag.joins(:taggings)
+       .merge(Tagging.where(taggable: taggables, context: context))
+       .distinct.order(:name).pluck(:name)
   end
 
   def unfeasible_or_unselected_filter