patch 9.0.0518: virtual text highlight starts too early with 'nowrap'

Problem:    Virtual text highlight starts too early with 'nowrap' and 'number'
            set.
Solution:   Add the offset to the attribute skip count. (issue #11138)
diff --git a/src/testdir/test_textprop.vim b/src/testdir/test_textprop.vim
index 452d9d2..ef612fa 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -2925,6 +2925,9 @@
   call term_sendkeys(buf, "\<Esc>:set number\<CR>")
   call VerifyScreenDump(buf, 'Test_prop_below_split_line_2', {})
 
+  call term_sendkeys(buf, ":set nowrap\<CR>")
+  call VerifyScreenDump(buf, 'Test_prop_below_split_line_3', {})
+
   call StopVimInTerminal(buf)
 endfunc