patch 8.0.1837: one character cmdline abbreviation not triggered after '<,'>

Problem:    One character cmdline abbreviation not triggered after '<,'>.
Solution:   Skip over the special range. (Christian Brabandt, closes #2320)
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index 79863c4..fd7e28f 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -214,3 +214,19 @@
   delfunc Eatchar
   bw!
 endfunc
+
+func Test_cabbr_visual_mode()
+  cabbr s su
+  call feedkeys(":s \<c-B>\"\<CR>", 'itx')
+  call assert_equal('"su ', getreg(':'))
+  call feedkeys(":'<,'>s \<c-B>\"\<CR>", 'itx')
+  let expected = '"'. "'<,'>su "
+  call assert_equal(expected, getreg(':'))
+  call feedkeys(":  '<,'>s \<c-B>\"\<CR>", 'itx')
+  let expected = '"  '. "'<,'>su "
+  call assert_equal(expected, getreg(':'))
+  call feedkeys(":'a,'bs \<c-B>\"\<CR>", 'itx')
+  let expected = '"'. "'a,'bsu "
+  call assert_equal(expected, getreg(':'))
+  cunabbr s
+endfunc