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)

Author: brammool

src/testdir/test_vim9_expr.vim

@@ -2426,6 +2426,10 @@ def Test_expr_member_vim9script()
   CheckScriptSuccess(lines)
 enddef
 
+def SetSomeVar()
+  b:someVar = &fdm
+enddef
+
 def Test_expr7_option()
   # option
   set ts=11
@@ -2443,6 +2447,11 @@ def Test_expr7_option()
   var bval: bool = &tgc
   var nval: number = &ts
   var sval: string = &path
+
+  # check v_lock is cleared (requires using valgrind, doesn't always show)
+  SetSomeVar()
+  b:someVar = 0
+  unlet b:someVar
 enddef
 
 def Test_expr7_environment()

src/typval.c

@@ -1117,6 +1117,7 @@ eval_option(
     }
     else if (rettv != NULL)
     {
+	rettv->v_lock = 0;
 	if (opt_type == gov_hidden_string)
 	{
 	    rettv->v_type = VAR_STRING;

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2302,
 /**/
     2301,
 /**/