Return early in Classifier.classify if no languages supplied (#3471)

* Return early if no languages supplied

There's no need to tokenise the data when attempting to classify without a limited language scope as no action will be performed when it comes to scoring anyway.

* Add test for empty languages array

lib/linguist/classifier.rb

@@ -95,7 +95,7 @@ module Linguist
     # Returns sorted Array of result pairs. Each pair contains the
     # String language name and a Float score.
     def classify(tokens, languages)
-      return [] if tokens.nil?
+      return [] if tokens.nil? || languages.empty?
       tokens = Tokenizer.tokenize(tokens) if tokens.is_a?(String)
       scores = {}
 

test/test_classifier.rb

@@ -53,4 +53,8 @@ class TestClassifier < Minitest::Test
       assert_equal language.name, results.first[0], "#{sample[:path]}\n#{results.inspect}"
     end
   end
+
+  def test_classify_empty_languages
+    assert_equal [], Classifier.classify(Samples.cache, fixture("Ruby/foo.rb"), [])
+  end
 end