patch 8.2.0625: Vim9: confusing error when calling unknown function

Problem:    Vim9: confusing error when calling unknown function.
Solution:   Give error while compiling.
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 8a6c3d6..d364679 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -193,10 +193,23 @@
 enddef
 
 def Test_call_func_defined_later()
-  call assert_equal('one', DefinedLater('one'))
+  call assert_equal('one', g:DefinedLater('one'))
   call assert_fails('call NotDefined("one")', 'E117:')
 enddef
 
+func DefinedLater(arg)
+  return a:arg
+endfunc
+
+def Test_call_funcref()
+  assert_equal(3, g:SomeFunc('abc'))
+  assert_fails('NotAFunc()', 'E117:')
+  assert_fails('g:NotAFunc()', 'E117:')
+enddef
+
+let SomeFunc = function('len')
+let NotAFunc = 'text'
+
 def CombineFuncrefTypes()
   " same arguments, different return type
   let Ref1: func(bool): string
@@ -217,12 +230,8 @@
   Refb3 = g:cond ? Refb1 : Refb2
 enddef
 
-func DefinedLater(arg)
-  return a:arg
-endfunc
-
 def FuncWithForwardCall()
-  return DefinedEvenLater("yes")
+  return g:DefinedEvenLater("yes")
 enddef
 
 def DefinedEvenLater(arg: string): string
@@ -372,9 +381,9 @@
   so Xdef
   call delete('Xdef')
 
-  call assert_equal(0, Func0())
-  call assert_equal('Func1', Func1())
-  call assert_equal('Func2', Func2())
+  call assert_equal(0, g:Func0())
+  call assert_equal('Func1', g:Func1())
+  call assert_equal('Func2', g:Func2())
 
   delfunc! Func0
   delfunc! Func1