tdehwlib: Fix the flag setting whether the storage device contains the file system.

This resolves bug 2232, bug 2607 and bug 2946.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit dfe3c9649f)

tdecore/tdehw/tdehardwaredevices.cpp

@@ -2697,7 +2697,7 @@ void TDEHardwareDevices::updateExistingDeviceInformation(TDEGenericDevice* exist
 				diskstatus = diskstatus | TDEDiskDeviceStatus::Hotpluggable;
 			}
 
-			if ((filesystemtype.upper() != "CRYPTO_LUKS") && (filesystemtype.upper() != "CRYPTO") && (filesystemtype.upper() != "SWAP") && (!filesystemtype.isNull())) {
+			if ((filesystemtype.upper() != "CRYPTO_LUKS") && (filesystemtype.upper() != "CRYPTO") && (filesystemtype.upper() != "SWAP") && (!filesystemtype.isEmpty())) {
 				diskstatus = diskstatus | TDEDiskDeviceStatus::ContainsFilesystem;
 			}
 			else {