patch 9.0.0811: error if :echowin is preceded by a command modifier

Problem:    Error if :echowin is preceded by a command modifier.
Solution:   Do not give an error for range when there is a modifier.
            (closes #11414)

src/testdir/test_vim9_script.vim

@@ -2032,6 +2032,10 @@ enddef
 def Test_echowindow_cmd()
   var local = 'local'
   echowindow 'something' local # comment
+
+  # with modifier
+  unsilent echowin 'loud'
+
   # output goes in message window
   popup_clear()
 enddef