patch 9.1.0447: completion may be wrong when deleting all chars

Problem:  completion may be wrong when deleting all chars
Solution: reset compl_shown_match

closes: #14854

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/insexpand.c

@@ -1255,6 +1255,12 @@ ins_compl_build_pum(void)
     if (match_at_original_text(compl_shown_match))
 	shown_match_ok = TRUE;
 
+    if (compl_leader != NULL
+	    && STRCMP(compl_leader, compl_orig_text) == 0
+	    && shown_match_ok == FALSE)
+	compl_shown_match = compl_no_select ? compl_first_match
+					    : compl_first_match->cp_next;
+
     i = 0;
     compl = compl_first_match;
     do

src/testdir/test_ins_complete.vim

@@ -630,7 +630,7 @@ func Test_pum_with_preview_win()
   CheckScreendump
 
   let lines =<< trim END
-      funct Omni_test(findstart, base)
+    func Omni_test(findstart, base)
       if a:findstart
         return col(".") - 1
       endif

src/testdir/test_popup.vim

@@ -1175,6 +1175,8 @@ func Test_CompleteChanged()
   set completeopt=menu,menuone
   call feedkeys("i\<C-X>\<C-O>\<BS>\<BS>\<BS>f", 'tx')
   call assert_equal('five', g:word)
+  call feedkeys("i\<C-X>\<C-O>\<BS>\<BS>\<BS>f\<BS>", 'tx')
+  call assert_equal('one', g:word)
 
   autocmd! AAAAA_Group
   set complete& completeopt&

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    447,
 /**/
     446,
 /**/