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/clientserver.c b/src/clientserver.c
index cf35c81..fbbeb6a 100644
--- a/src/clientserver.c
+++ b/src/clientserver.c
@@ -86,7 +86,7 @@
     // to be typed.  Do generate errors so that try/catch works.
     ++emsg_silent;
 
-    res = eval_to_string(expr, NULL, TRUE);
+    res = eval_to_string(expr, TRUE);
 
     debug_break_level = save_dbl;
     redir_off = save_ro;