patch 8.1.2373: cannot build with +popupwin but without +quickfix

Problem:    Cannot build with +popupwin but without +quickfix. (John Marriott)
Solution:   Adjust #ifdefs.
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index b205b9d..5634b98 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1548,6 +1548,7 @@
 
 func Test_write_to_deleted_buffer()
   CheckExecutable echo
+  CheckFeature quickfix
 
   let job = job_start('echo hello', {'out_io': 'buffer', 'out_name': 'test_buffer', 'out_msg': 0})
   let bufnr = bufnr('test_buffer')