patch 8.2.0367: can use :pedit in a popup window

Problem:    Can use :pedit in a popup window.
Solution:   Disallow it.
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index d89824d..9cd6e32 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -926,6 +926,7 @@
   call assert_fails('call win_execute(winid, "tabnext")', 'E994:')
   call assert_fails('call win_execute(winid, "next")', 'E994:')
   call assert_fails('call win_execute(winid, "rewind")', 'E994:')
+  call assert_fails('call win_execute(winid, "pedit filename")', 'E994:')
   call assert_fails('call win_execute(winid, "buf")', 'E994:')
   call assert_fails('call win_execute(winid, "bnext")', 'E994:')
   call assert_fails('call win_execute(winid, "bprev")', 'E994:')