Correct Unix QStorageInfo's QStorageIterator::next()'s loop logic

The loop was accepting any line with at least three entries, but the
code that then used this line needed four entries.  At the same time,
the loop's check had to be repeated, in rearranged form, after the
loop, to handle some failing cases.  Restructuring the loop, and
demanding at least four entries, fixes all of this, although care must
be taken about the virtual file-system lying about .atEnd().

[ChangeLog][QtCore][QStorageInfo] Fixed a bug on Android that could
cause QStorageInfo to skip some filesystems (if the mount table is a
virtual file and contains any short lines) or crash (if the mount
table contains any 3-field lines).

Change-Id: I1c2674372d0d0b7d16937de4345a910bc7d6e0ad
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Ivan Komissarov <ABBAPOH@gmail.com>
Reviewed-by: Johannes Rosenqvist <xeroc81@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qstorageinfo_unix.cpp

@@ -342,13 +342,14 @@ inline bool QStorageIterator::isValid() const
 inline bool QStorageIterator::next()
 {
     QList<QByteArray> data;
+    // If file is virtual, file.readLine() may succeed even when file.atEnd().
     do {
         const QByteArray line = file.readLine();
-        data = line.split(' ');
-    } while (data.count() < 3 && !file.atEnd());
-
-    if (file.atEnd() && data.count() <= 3)
+        if (line.isEmpty() && file.atEnd())
             return false;
+        data = line.split(' ');
+    } while (data.count() < 4);
+
     m_device = data.at(0);
     m_rootPath = data.at(1);
     m_fileSystemType = data.at(2);