Include blank and null ballots in booth totals

Just the same way it's done for all polls.

spec/helpers/poll_recounts_helper_spec.rb

@@ -0,0 +1,13 @@
+require "rails_helper"
+
+describe PollRecountsHelper do
+  describe "#total_recounts_by_booth" do
+    it "includes blank and null votes" do
+      assignment = create(:poll_booth_assignment)
+      create(:poll_recount, :from_booth, booth_assignment: assignment, total_amount: 3, white_amount: 1)
+      create(:poll_recount, :from_booth, booth_assignment: assignment, total_amount: 4, null_amount: 2)
+
+      expect(total_recounts_by_booth(assignment)).to eq 10
+    end
+  end
+end