patch 8.2.2116: MS-Windows GUI: test for 'guifont' is incomplete

Problem:    MS-Windows GUI: test for 'guifont' is incomplete.
Solution:   Set 'renderoptions'. (Christian Brabandt)
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 6d750e0..0d504d5 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -386,13 +386,18 @@
   if has('win32')
     " Invalid font names are accepted in GTK GUI
     call assert_fails('set guifont=xa1bc23d7f', 'E596:')
+  endif
 
+  if exists('+renderoptions')
     " doing this four times used to cause a crash
-    set guifont=
-    set guifont=
-    set guifont=
-    set guifont=
-    set guifont=
+    set renderoptions=type:directx
+    for i in range(5)
+      set guifont=
+    endfor
+    set renderoptions=
+    for i in range(5)
+      set guifont=
+    endfor
   endif
 
   if has('xfontset')