patch 8.0.0264: memory error reported by ubsan

Problem:    Memory error reported by ubsan, probably for using the string
            returned by execute().
Solution:   NUL terminate the result of execute().

Author: brammool

src/evalfunc.c

@@ -2819,7 +2819,17 @@ f_execute(typval_T *argvars, typval_T *rettv)
 	--list->lv_refcount;
     }
 
-    rettv->vval.v_string = redir_execute_ga.ga_data;
+    /* Need to append a NUL to the result. */
+    if (ga_grow(&redir_execute_ga, 1) == OK)
+    {
+	((char *)redir_execute_ga.ga_data)[redir_execute_ga.ga_len] = NUL;
+	rettv->vval.v_string = redir_execute_ga.ga_data;
+    }
+    else
+    {
+	ga_clear(&redir_execute_ga);
+	rettv->vval.v_string = NULL;
+    }
     msg_silent = save_msg_silent;
     emsg_silent = save_emsg_silent;
     emsg_noredir = save_emsg_noredir;

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    264,
 /**/
     263,
 /**/