patch 8.2.3405: cannot have a comment line in a {} block of a user command

Problem:    Cannot have a comment line in a {} block of a user command.
Solution:   Continue after the line break. (closes #8837)

src/ex_docmd.c

@@ -2807,7 +2807,16 @@ parse_command_modifiers(
 
 	// ignore comment and empty lines
 	if (comment_start(eap->cmd, starts_with_colon))
+	{
+	    // a comment ends at a NL
+	    if (eap->nextcmd == NULL)
+	    {
+		eap->nextcmd = vim_strchr(eap->cmd, '\n');
+		if (eap->nextcmd != NULL)
+		    ++eap->nextcmd;
+	    }
 	    return FAIL;
+	}
 	if (*eap->cmd == NUL)
 	{
 	    if (!skip_only)

src/testdir/test_usercommands.vim

@@ -624,7 +624,8 @@ endfunc
 
 func Test_usercmd_with_block()
   command DoSomething {
-        g:didit = 'yes'
+        g:didit = 'yes'  # comment
+        # comment line
         g:didmore = 'more'
       }
   DoSomething

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3405,
 /**/
     3404,
 /**/