Add some error handling for the inotify file system watcher

In the readFromInotify() function, add a check whether
the ioctl function is successful or not. In the case of
failure, continuing to execute the following code would cause
errors in the read function because there is no data in the buffer.

Change-Id: Id53037e9e48c97c9eb75835048143875275b6370
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/io/qfilesystemwatcher_inotify.cpp

@@ -366,7 +366,9 @@ void QInotifyFileSystemWatcherEngine::readFromInotify()
     // qDebug("QInotifyFileSystemWatcherEngine::readFromInotify");
 
     int buffSize = 0;
-    ioctl(inotifyFd, FIONREAD, (char *) &buffSize);
+    if (ioctl(inotifyFd, FIONREAD, (char *) &buffSize) == -1)
+        return;
+
     QVarLengthArray<char, 4096> buffer(buffSize);
     buffSize = read(inotifyFd, buffer.data(), buffSize);
     char *at = buffer.data();