Fix for MDEV-14141 Crash in print_keydup_error()

May also fix: MDEV-14970 "MariaDB crashed with signal 11 and Aria table"

I am not able to reproduce a crash, however there was no protection in
print_keydup_error() if the storage engine reported the wrong key number.

This patch adds such a protection and should stop any further crashes
in this case.

Other things:
- Added extra protection in Aria to not set errkey to more than number of
  keys. (Don't think this is cause of this crash, but better safe than
  sorry)
- Extend test_if_equal_repl_errors() to handle different cases of
  ER_DUP_ENTRY. This is just mainly precaution for the future.

sql/handler.cc

@@ -3338,9 +3338,11 @@ void print_keydup_error(TABLE *table, KEY *key, const char *msg, myf errflag)
 
   if (key == NULL)
   {
-    /* Key is unknown */
-    str.copy("", 0, system_charset_info);
-    my_printf_error(ER_DUP_ENTRY, msg, errflag, str.c_ptr(), "*UNKNOWN*");
+    /*
+      Key is unknown. Should only happen if storage engine reports wrong
+      duplicate key number.
+    */
+    my_printf_error(ER_DUP_ENTRY, msg, errflag, "", "*UNKNOWN*");
   }
   else
   {
@@ -3432,11 +3434,9 @@ void handler::print_error(int error, myf errflag)
     if (table)
     {
       uint key_nr=get_dup_key(error);
-      if ((int) key_nr >= 0)
+      if ((int) key_nr >= 0 && key_nr < table->s->keys)
       {
-        print_keydup_error(table,
-                           key_nr == MAX_KEY ? NULL : &table->key_info[key_nr],
-                           errflag);
+        print_keydup_error(table, &table->key_info[key_nr], errflag);
         DBUG_VOID_RETURN;
       }
     }