patch 8.1.0279: 'incsearch' highlighting does not skip white space

Problem:    'incsearch' highlighting does not skip white space.
Solution:   Skip white space after the command. (issue #3321)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index 38e46cc..05046b3 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -868,8 +868,14 @@
   call term_sendkeys(buf, ':5,2s/foo')
   sleep 100m
   call VerifyScreenDump(buf, 'Test_incsearch_substitute_04', {})
-
   call term_sendkeys(buf, "\<Esc>")
+
+  " White space after the command is skipped
+  call term_sendkeys(buf, ':2,3sub  /fo')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_substitute_05', {})
+  call term_sendkeys(buf, "\<Esc>")
+
   call StopVimInTerminal(buf)
   call delete('Xis_subst_script')
 endfunc