patch 8.2.2835: Vim9: leaking memory in :cexpr

Problem:    Vim9: leaking memory in :cexpr.
Solution:   Also free the command line copy.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 607f651..ead193f 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -9641,6 +9641,7 @@
 	    break;
 
 	case ISN_CEXPR_CORE:
+	    vim_free(isn->isn_arg.cexpr.cexpr_ref->cer_cmdline);
 	    vim_free(isn->isn_arg.cexpr.cexpr_ref);
 	    break;