patch 8.2.3923: Vim9: double free with split argument list in nested function

Problem:    Vim9: double free if a nested function has a line break in the
            argument list.
Solution:   Set cmdlinep when freeing the previous line.
diff --git a/src/userfunc.c b/src/userfunc.c
index e1028e7..a7cbac3 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -219,6 +219,8 @@
 	    if (theline == NULL)
 		break;
 	    vim_free(*line_to_free);
+	    if (*eap->cmdlinep == *line_to_free)
+		*eap->cmdlinep = theline;
 	    *line_to_free = theline;
 	    whitep = (char_u *)" ";
 	    p = skipwhite(theline);