patch 8.2.4771: Coverity warns for not checking return value

Problem:    Coverity warns for not checking return value.
Solution:   Check return value of rettv_dict_alloc().

src/channel.c

@@ -4549,7 +4549,8 @@ ch_expr_common(typval_T *argvars, typval_T *rettv, int eval)
 	dictitem_T	*di;
 
 	// return an empty dict by default
-	rettv_dict_alloc(rettv);
+	if (rettv_dict_alloc(rettv) == FAIL)
+	    return;
 
 	if (argvars[1].v_type != VAR_DICT)
 	{

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4771,
 /**/
     4770,
 /**/