QStorageInfo/Linux: remove unnecessary isSymlink() call

symlinkTarget() suffices, because if the candidate is not a symlink, it
will return an empty string. Plus, /dev/disks/by-label is a udev-managed
directory, so everything should be a symlink.

This doesn't change the number of statx() calls because QDirIterator
needs some information on file types to decide how to filter and,
unfortunately, that information is missing for symlinks (we know it's a
symlink, but we don't know what it points to). Moreover, due to
QDirIterator's design, we always statx() one entry past the one we
wanted.

Pick-to: 6.6
Change-Id: I9d43e5b91eb142d6945cfffd1786ce1bd3398d1b
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qstorageinfo_linux.cpp

@@ -65,11 +65,13 @@ static inline QString retrieveLabel(const QByteArray &device)
 
     QFileInfo devinfo(QFile::decodeName(device));
     QString devicePath = devinfo.canonicalFilePath();
+    if (devicePath.isEmpty())
+        return QString();
 
     QDirIterator it(QLatin1StringView(pathDiskByLabel), QDir::NoDotAndDotDot);
     while (it.hasNext()) {
         QFileInfo fileInfo = it.nextFileInfo();
-        if (fileInfo.isSymLink() && fileInfo.symLinkTarget() == devicePath)
+        if (fileInfo.symLinkTarget() == devicePath)
             return decodeFsEncString(fileInfo.fileName());
     }
     return QString();