patch 9.0.0221: accessing freed memory if compiling nested function fails

Problem:    Accessing freed memory if compiling nested function fails.
Solution:   Mess up the variable name so that it won't be found.

src/testdir/test_vim9_func.vim

@@ -911,6 +911,18 @@ def Test_nested_function()
   v9.CheckScriptFailure(lines, 'E1173: Text found after enddef: burp', 3)
 enddef
 
+def Test_nested_function_fails()
+  var lines =<< trim END
+      def T()
+        def Func(g: string):string
+        enddef
+        Func()
+      enddef
+      silent! defcompile
+  END
+  v9.CheckScriptFailure(lines, 'E1069:')
+enddef
+
 def Test_not_nested_function()
   echo printf('%d',
       function('len')('xxx'))

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    221,
 /**/
     220,
 /**/

src/vim9compile.c

@@ -830,6 +830,7 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx, garray_T *lines_to_free)
     int		r = FAIL;
     compiletype_T   compile_type;
     isn_T	*funcref_isn = NULL;
+    lvar_T	*lvar = NULL;
 
     if (eap->forceit)
     {
@@ -936,9 +937,8 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx, garray_T *lines_to_free)
     else
     {
 	// Define a local variable for the function reference.
-	lvar_T	*lvar = reserve_local(cctx, func_name, name_end - name_start,
+	lvar = reserve_local(cctx, func_name, name_end - name_start,
 						    TRUE, ufunc->uf_func_type);
-
 	if (lvar == NULL)
 	    goto theend;
 	if (generate_FUNCREF(cctx, ufunc, &funcref_isn) == FAIL)
@@ -957,6 +957,9 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx, garray_T *lines_to_free)
 	    && compile_def_function(ufunc, TRUE, compile_type, cctx) == FAIL)
     {
 	func_ptr_unref(ufunc);
+	if (lvar != NULL)
+	    // Now the local variable can't be used.
+	    *lvar->lv_name = '/';  // impossible value
 	goto theend;
     }