patch 8.2.3966: when using feedkeys() abbreviations may be blocked

Problem:    When using feedkeys() abbreviations may be blocked.
Solution:   Reset tb_no_abbr_cnt when running out of characters.
            (closes #9448)

src/testdir/test_feedkeys.vim

@@ -13,4 +13,14 @@ func Test_feedkeys_x_with_empty_string()
   quit!
 endfunc
 
+func Test_feedkeys_with_abbreviation()
+  new
+  inoreabbrev trigger value
+  call feedkeys("atrigger ", 'x')
+  call feedkeys("atrigger ", 'x')
+  call assert_equal('value value ', getline(1))
+  bwipe!
+  iunabbrev trigger
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab