patch 8.2.1178: Vim9: filter function recognized as command modifier

Problem:    Vim9: filter function recognized as command modifier, leading to a
            crash.
Solution:   Clear cmdmod after freeing items.  Do not recognize a command
            modifier followed by non-white space. (closes #6434)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index e7f90e1..8905ee3 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -6963,6 +6963,7 @@
 	}
 	// TODO: use modifiers in the command
 	undo_cmdmod(&ea, save_msg_scroll);
+	CLEAR_FIELD(cmdmod);
 
 	// Skip ":call" to get to the function name.
 	if (checkforcmd(&ea.cmd, "call", 3))