Allow split description strings in ExampleDescription

Splitting the description string after `it` with a `+` is
not normal, but it can occur during auto-correction as an
intermediate state of the source code. Make sure the cop
doesn't crash.

lib/rubocop/cop/internal_affairs/example_description.rb

@@ -80,10 +80,14 @@ def on_send(node)
         private
 
         def check_description(description, regexps, message)
-          return unless regexps.any? { |regexp| regexp.match?(description.value) }
+          return unless regexps.any? { |regexp| regexp.match?(string_contents(description)) }
 
           add_offense(description, message: message)
         end
+
+        def string_contents(node)
+          node.str_type? ? node.value : node.source
+        end
       end
     end
   end

spec/rubocop/cop/internal_affairs/example_description_spec.rb

@@ -46,6 +46,14 @@
       RUBY
     end
 
+    it 'does not crash when given a proper description that is split with +' do
+      expect_no_offenses(<<~RUBY)
+        it "does " + 'not register an offense' do
+          expect_no_offense('code')
+        end
+      RUBY
+    end
+
     it 'does not register an offense when given an unexpected description' do
       expect_no_offenses(<<~RUBY)
         it 'foo bar baz' do