FIX: Don’t raise on some search terms

Currently, when certain search terms are provided, this can lead to
`Search.need_segmenting?` raising an error because it makes `URI#path`
to return `nil` instead of a string.

This patch forces a cast to string so it won’t raise anymore.

spec/lib/search_spec.rb

@@ -31,6 +31,14 @@ RSpec.describe Search do
         it { is_expected.not_to be_need_segmenting(data) }
       end
 
+      context "when data makes `URI#path` return `nil`" do
+        let(:data) { "in:solved%20category:50%20order:likes" }
+
+        it "doesn’t raise an error" do
+          expect { search.need_segmenting?(data) }.not_to raise_error
+        end
+      end
+
       context "when data is something else" do
         let(:data) { "text" }