patch 9.1.1762: completion: selected item not cleared on <BS> with 'ac'

Problem:  completion: selected item not cleared on backspace when
          'autocomplete' is set
Solution: Clear the selected item (Girish Palya)

closes: #18260

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/insexpand.c

@@ -2424,6 +2424,10 @@ ins_compl_bs(void)
 	return K_BS;
     }
 
+    // Clear selection if a menu item is currently selected in autocompletion
+    if (compl_autocomplete && compl_first_match)
+	compl_shown_match = compl_first_match;
+
     ins_compl_new_leader();
     if (compl_shown_match != NULL)
 	// Make sure current match is not a hidden item.

src/testdir/test_ins_complete.vim

@@ -5247,6 +5247,21 @@ func Test_autocomplete_trigger()
   call feedkeys("Sazx\<Left>\<BS>\<F2>\<Esc>0", 'tx!')
   call assert_equal(['and', 'afoo'], b:matches->mapnew('v:val.word'))
 
+  " Test 6: <BS> should clear the selected item
+  %d
+  call setline(1, ["foobarfoo", "foobar", "foobarbaz"])
+  call feedkeys("Gofo\<C-N>\<C-N>\<F2>\<F3>\<Esc>0", 'tx!')
+  call assert_equal(['foobarbaz', 'foobar', 'foobarfoo'], b:matches->mapnew('v:val.word'))
+  call assert_equal(1, b:selected)
+  call feedkeys("Sfo\<C-N>\<C-N>\<BS>\<F2>\<F3>\<Esc>0", 'tx!')
+  call assert_equal(['foobarbaz', 'foobar', 'foobarfoo'], b:matches->mapnew('v:val.word'))
+  call assert_equal(-1, b:selected)
+  call assert_equal('fooba', getline(4))
+  call feedkeys("Sfo\<C-N>\<C-N>\<BS>\<C-N>\<F2>\<F3>\<Esc>0", 'tx!')
+  call assert_equal(['foobarbaz', 'foobar', 'foobarfoo'], b:matches->mapnew('v:val.word'))
+  call assert_equal(0, b:selected)
+  call assert_equal('foobarbaz', getline(4))
+
   bw!
   call test_override("char_avail", 0)
   delfunc NonKeywordComplete

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1762,
 /**/
     1761,
 /**/