patch 8.2.1049: Vim9: leaking memory when using continuation line

Problem:    Vim9: leaking memory when using continuation line.
Solution:   Keep a pointer to the continuation line in evalarg_T.  Centralize
            checking for a next command.
diff --git a/src/if_perl.xs b/src/if_perl.xs
index bf269cb..cad571c 100644
--- a/src/if_perl.xs
+++ b/src/if_perl.xs
@@ -832,7 +832,6 @@
     char_u *
 eval_to_string(
     char_u	*arg UNUSED,
-    char_u	**nextcmd UNUSED,
     int		dolist UNUSED)
 {
     return NULL;
@@ -1562,7 +1561,7 @@
     PREINIT:
 	char_u *value;
     PPCODE:
-	value = eval_to_string((char_u *)str, (char_u **)0, TRUE);
+	value = eval_to_string((char_u *)str, TRUE);
 	if (value == NULL)
 	{
 	    XPUSHs(sv_2mortal(newSViv(0)));