patch 9.1.0830: using wrong highlight group for spaces for popupmenu

Problem:  using wrong highlight group for spaces for popupmenu
Solution: use original attribute instead of combined attributed
          (glepnir)

closes: #15978

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 3c748a4..6b807c8 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -1507,10 +1507,18 @@
 func Test_pum_user_abbr_hlgroup()
   CheckScreendump
   let lines =<< trim END
-    func CompleteFunc( findstart, base )
+    let s:var = 0
+    func CompleteFunc(findstart, base)
       if a:findstart
         return 0
       endif
+      if s:var == 1
+        return {
+              \ 'words': [
+              \ { 'word': 'aword1', 'abbr_hlgroup': 'StrikeFake' },
+              \ { 'word': '你好', 'abbr_hlgroup': 'StrikeFake' },
+              \]}
+      endif
       return {
             \ 'words': [
             \ { 'word': 'aword1', 'menu': 'extra text 1', 'kind': 'W', 'abbr_hlgroup': 'StrikeFake' },
@@ -1518,6 +1526,9 @@
             \ { 'word': '你好', 'menu': 'extra text 3', 'kind': 'W', 'abbr_hlgroup': 'StrikeFake' },
             \]}
     endfunc
+    func ChangeVar()
+      let s:var = 1
+    endfunc
     set completeopt=menu
     set completefunc=CompleteFunc
 
@@ -1545,13 +1556,20 @@
   call VerifyScreenDump(buf, 'Test_pum_highlights_14', {})
   call term_sendkeys(buf, "\<C-E>\<Esc>")
 
+  call TermWait(buf)
+  call term_sendkeys(buf, ":call ChangeVar()\<CR>")
+  call TermWait(buf)
+  call term_sendkeys(buf, "S\<C-X>\<C-U>")
+  call VerifyScreenDump(buf, 'Test_pum_highlights_17', {})
+  call term_sendkeys(buf, "\<C-E>\<Esc>")
+
   call StopVimInTerminal(buf)
 endfunc
 
 func Test_pum_user_kind_hlgroup()
   CheckScreendump
   let lines =<< trim END
-    func CompleteFunc( findstart, base )
+    func CompleteFunc(findstart, base)
       if a:findstart
         return 0
       endif