Do not create modal message boxes for broken files
When a broken file(1) is loaded the FileManager class in the marble library open a modal error dialog. This is especially bad for non-interactive contexts, e.g. the thumbnailer. Opening a folder with non-parseable files in dolphin may spawn dozens of error dialogs.
Broken files includes both malformed files (e.g. with encoding errors, see https://bugs.kde.org/show_bug.cgi?id=416925), or files with mimetype mismatches (https://bugs.kde.org/show_bug.cgi?id=420089).
Also stop waiting for the 5 second timeout in the thumbnailer.