patch 8.1.2198: crash when using :center in autocommand

Problem:    Crash when using :center in autocommand.
Solution:   Bail out early for an empty line. (Dominique pelle, closes #5095)
diff --git a/src/testdir/test_textformat.vim b/src/testdir/test_textformat.vim
index 13fb50b..3a0552b 100644
--- a/src/testdir/test_textformat.vim
+++ b/src/testdir/test_textformat.vim
@@ -1,4 +1,7 @@
 " Tests for the various 'formatoptions' settings
+
+source check.vim
+
 func Test_text_format()
   enew!
 
@@ -489,3 +492,20 @@
   bwipe!
   set fo& ai& bs&
 endfunc
+
+func Test_crash_github_issue_5095()
+  CheckFeature autocmd
+
+  " This used to segfault, see https://github.com/vim/vim/issues/5095
+  augroup testing
+    au BufNew x center
+  augroup END
+
+  next! x
+
+  bw
+  augroup testing
+    au!
+  augroup END
+  augroup! testing
+endfunc