vim-patch:8.2.3329: v_lock not set when getting value of environment variable

Problem:    v_lock not set when getting value of environment variable.
Solution:   Set v_lock to zero.

16e63e6d35

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

src/nvim/eval.c

@@ -4918,6 +4918,7 @@ static int eval_env_var(char **arg, typval_T *rettv, int evaluate)
     name[len] = (char)cc;
     rettv->v_type = VAR_STRING;
     rettv->vval.v_string = string;
+    rettv->v_lock = VAR_UNLOCKED;
   }
 
   return OK;