patch 8.2.3449: sort fails if the sort compare function returns 999

Problem:    Sort fails if the sort compare function returns 999.
Solution:   Adjust value to -1 / 0 / 1. (Yasuhiro Matsumoto, closes #8884)

Author: mattn

src/list.c

@@ -1945,7 +1945,13 @@ item_compare2(const void *s1, const void *s2)
     if (res == FAIL)
 	res = ITEM_COMPARE_FAIL;
     else
+    {
 	res = (int)tv_get_number_chk(&rettv, &sortinfo->item_compare_func_err);
+	if (res > 0)
+	    res = 1;
+	else if (res < 0)
+	    res = -1;
+    }
     if (sortinfo->item_compare_func_err)
 	res = ITEM_COMPARE_FAIL;  // return value has wrong type
     clear_tv(&rettv);

src/testdir/test_sort.vim

@@ -58,6 +58,7 @@ endfunc
 func Test_sort_numbers()
   call assert_equal([3, 13, 28], sort([13, 28, 3], 'N'))
   call assert_equal(['3', '13', '28'], sort(['13', '28', '3'], 'N'))
+  call assert_equal([3997, 4996], sort([4996, 3997], 'Compare1'))
 endfunc
 
 func Test_sort_float()

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3449,
 /**/
     3448,
 /**/