Silent failure on long pathname

bug-fixed

#1

Folder load (Explorer right-click of folder, click Mp3tag) can silently fail on files with long folderpaths e.g.
D:\AppData\My Dropbox\KLIB TINTing\KLIB_1_A-C\iTunes Music\Berliner Philharmoniker, Chor Der Deutschen Oper Berlin, Edith Mathis, Francisco Araiza, Gottfried Hornik, Herbert von Karajan, Janet Perry, José Van Dam & Karin Ott\Mozart_ Die Zauberfasdlöte (Highlights)\15 Die Zauberflöte, K. 620_ Pa-Pa-Pa-Pa-Pa-Pa-Papagena!.flac

This is really bad. It leaves the user believing all the files are in Mp3tag when secretly some are missing.

If Mp3tag cannot fulfill an instruction that it has accepted, it MUST issue a warning.

Note: this slightly shorter path does not fail:

D:\AppData\My Dropbox\KLIB TINTing\KLIB_1\iTunes Music\Berliner Philharmoniker, Chor Der Deutschen Oper Berlin, Edith Mathis, Francisco Araiza, Gottfried Hornik, Herbert von Karajan, Janet Perry, José Van Dam & Karin Ott\Mozart_ Die Zauberfasdlöte (Highlights)\15 Die Zauberflöte, K. 620_ Pa-Pa-Pa-Pa-Pa-Pa-Papagena!.flac

Note: a fast check to verify load is not failing this way: count the number of tracks first in another program e.g. Beyond Compare, then when the Mp3tag load's "Reading directory" dialog appears, verify this display of the total qty of files is equal.