[BUGFIX] Optimize memory consumption by fetching from \mysqli_result

Followup on #27
Could you leave this line in, instead of the new line 107? It's nicer to see a percentage instead of all these numbers flashing by when migrating a lot of files. Also, this message is only shown when a file is actually processed and not on all failures (message on line 107 shows allways).

Sorry, but we'll get there . . . ;-)