patch 8.2.2302: Vim9: using an option value may use uninitialized memory

Problem:    Vim9: using an option value may use uninitialized memory.
Solution:   Clear v_lock. (closes #7620)
diff --git a/src/typval.c b/src/typval.c
index 421e62a..d16f0e6 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -1117,6 +1117,7 @@
     }
     else if (rettv != NULL)
     {
+	rettv->v_lock = 0;
 	if (opt_type == gov_hidden_string)
 	{
 	    rettv->v_type = VAR_STRING;