QInotifyFileSystemWatcherEngine::addPaths rejects valid watch descriptors.

There is an error in the QInotifyFileSystemWatcherEngine::addPaths function. The function attempts to register a file for watching and then checks whether the returned descriptor is valid like in the following pseudo-code fragment:
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int wd = inotify_add_watch([...]);
if (wd <= 0)

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The problem is that this treats a return value of 0 as invalid. According to the inotify_add_watch man page, a 0 is a valid value. Current versions of Linux do not actually return 0, for compatibility with programs which came to rely on 0 not being returned. Nevertheless that value could be returned in principle (Compare http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=08e53fcb0db34baca3db84a457b6d67faabee4c6).