patch 8.2.0347: various code not covered by tests

Problem:    Various code not covered by tests.
Solution:   Add more test coverage. (Yegappan Lakshmanan, closes #5720)
diff --git a/src/testdir/gen_opt_test.vim b/src/testdir/gen_opt_test.vim
index 91415e4..c3b2325 100644
--- a/src/testdir/gen_opt_test.vim
+++ b/src/testdir/gen_opt_test.vim
@@ -150,7 +150,7 @@
       \ 'viminfo': [['', '''50', '"30'], ['xxx']],
       \ 'virtualedit': [['', 'all', 'all,block'], ['xxx']],
       \ 'whichwrap': [['', 'b,s', 'bs'], ['xxx']],
-      \ 'wildmode': [['', 'full', 'list:full', 'full,longest'], ['xxx']],
+      \ 'wildmode': [['', 'full', 'list:full', 'full,longest'], ['xxx', 'a4', 'full,full,full,full,full']],
       \ 'wildoptions': [['', 'tagfile'], ['xxx']],
       \ 'winaltkeys': [['menu', 'no'], ['', 'xxx']],
       \