Fix for drive SQLMIX

[Itamar Lins]

Hi!

Here is the fix I applied to `sqlbase.c` to solve the SQLMIX issue:
```
static HB_ERRCODE sqlbaseInfo( SQLBASEAREAP pArea, HB_USHORT uiIndex, PHB_ITEM pItem )
{
   switch( uiIndex )
   {
      case DBI_QUERY:
         hb_itemPutC( pItem, pArea->szQuery );
         break;

      case DBI_ISREADONLY:
         hb_itemPutL( pItem, HB_FALSE );
         break;

      default:
         return SUPER_INFO( &pArea->area, uiIndex, pItem );
   }

   return HB_SUCCESS;
}
```

This ensures the SQLMIX RDD correctly returns a logical `.F.` instead of `Nil` when checked for read-only status, preventing errors in visual libraries like HWGui.

Best regards,
Itamar M. Lins Jr.