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/ex_docmd.c b/src/ex_docmd.c
index 0573897..692192b 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2750,6 +2750,10 @@
 				if (*p == NUL || ends_excmd(*p))
 				    break;
 			    }
+			    // Avoid that "filter(arg)" is recognized.
+			    if (in_vim9script() && !VIM_ISWHITE(*p))
+				break;
+
 			    if (skip_only)
 				p = skip_vimgrep_pat(p, NULL, NULL);
 			    else
@@ -2904,7 +2908,7 @@
 }
 
 /*
- * Unod and free contents of "cmdmod".
+ * Undo and free contents of "cmdmod".
  */
     void
 undo_cmdmod(exarg_T *eap, int save_msg_scroll)