patch 8.1.0278: 'incsearch' highlighting does not accept reverse range

Problem:    'incsearch' highlighting does not accept reverse range.
Solution:   Swap the range when needed. (issue #3321)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index 9b70126..38e46cc 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -862,6 +862,12 @@
   call term_sendkeys(buf, "\<BS>")
   sleep 100m
   call VerifyScreenDump(buf, 'Test_incsearch_substitute_03', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  " Reverse range is accepted
+  call term_sendkeys(buf, ':5,2s/foo')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_substitute_04', {})
 
   call term_sendkeys(buf, "\<Esc>")
   call StopVimInTerminal(buf)