[ie/youtube] Fix nsig and signature extraction for player 643afba4 (#12684)

Closes #12677, Closes #12682
Authored by: seproDev, bashonly

Co-authored-by: bashonly <88596187+bashonly@users.noreply.github.com>

test/test_jsinterp.py

@@ -462,6 +462,16 @@ class TestJSInterpreter(unittest.TestCase):
         ]:
             assert js_number_to_string(test, radix) == expected
 
+    def test_extract_function(self):
+        jsi = JSInterpreter('function a(b) { return b + 1; }')
+        func = jsi.extract_function('a')
+        self.assertEqual(func([2]), 3)
+
+    def test_extract_function_with_global_stack(self):
+        jsi = JSInterpreter('function c(d) { return d + e + f + g; }')
+        func = jsi.extract_function('c', {'e': 10}, {'f': 100, 'g': 1000})
+        self.assertEqual(func([1]), 1111)
+
 
 if __name__ == '__main__':
     unittest.main()