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)
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 6c8f1f0..58e214c 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -2032,6 +2032,10 @@
 def Test_echowindow_cmd()
   var local = 'local'
   echowindow 'something' local # comment
+
+  # with modifier
+  unsilent echowin 'loud'
+
   # output goes in message window
   popup_clear()
 enddef
diff --git a/src/version.c b/src/version.c
index 4017c47..662835e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    811,
+/**/
     810,
 /**/
     809,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 73bfa6c..fb66a78 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -2712,8 +2712,9 @@
 	;
     if (!isdigit(*p))
     {
-	// the command must be following
-	if (p < eap->cmd)
+	// The command or modifiers must be following.  Assume a lower case
+	// character means there is a modifier.
+	if (p < eap->cmd && !vim_islower(*p))
 	{
 	    emsg(_(e_invalid_range));
 	    return -1;