vim-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.

b171fb1790

Omit eval_next_line(): Vim9 script only.

vim-patch:8.2.1050: missing change in struct

Problem:    Missing change in struct.
Solution:   Add missing change.

65a8ed37f7

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval/vars.c

@@ -259,7 +259,7 @@ void ex_let(exarg_T *eap)
       .eval_flags = eap->skip ? 0 : EVAL_EVALUATE,
       .eval_cookie = eap->getline == getsourceline ? eap->cookie : NULL,
     };
-    i = eval0(expr, &rettv, &eap->nextcmd, &evalarg);
+    i = eval0(expr, &rettv, eap, &evalarg);
     if (eap->skip) {
       emsg_skip--;
     }