patch 8.1.1765: get(func, dict, def) does not work properly

Problem:    get(func, dict, def) does not work properly.
Solution:   Handle NULL dict better. (Takuya Fujiwara, closes #4734)
diff --git a/src/testdir/test_partial.vim b/src/testdir/test_partial.vim
index b180510..e7a7d05 100644
--- a/src/testdir/test_partial.vim
+++ b/src/testdir/test_partial.vim
@@ -320,6 +320,11 @@
   call assert_equal('MyDictFunc', get(Func, 'name'))
   call assert_equal([], get(Func, 'args'))
   call assert_true(empty( get(Func, 'dict')))
+
+  let P = function('substitute', ['hello there', 'there'])
+  let dict = {'partial has': 'no dict'}
+  call assert_equal(dict, get(P, 'dict', dict))
+  call assert_equal(0, get(l:P, 'dict'))
 endfunc
 
 func Test_compare_partials()