Fix root disk icon change so that it doesn't erroneously change other icons

Summary:
I committed D16653 too soon without enough testing, because it had the effect of applying the default `drive-harddisk` icon to more device types. Oops. Sorry about that. :(

This patch fixes the problem, and is better tested.

Test Plan:
Other device types are not affected:
{F6392616}

Reviewers: bruns, broulik, davidedmundson

Reviewed By: broulik

Subscribers: kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D16678

src/solid/devices/backends/udisks2/udisksdevice.cpp

@@ -614,11 +614,8 @@ QString Device::icon() const
 
     if (!iconName.isEmpty()) {
         return iconName;
-    } else if (queryDeviceInterface(Solid::DeviceInterface::StorageAccess)) {
-        const UDisks2::StorageAccess accessIface(const_cast<Device *>(this));
-        if (accessIface.filePath() == QLatin1String("/")) {
-            return QStringLiteral("drive-harddisk-root");
-        }
+    } else if (isRoot()) {
+        return QStringLiteral("drive-harddisk-root");
     } else if (isLoop()) {
         const QString backingFile = prop("BackingFile").toString();
         if (!backingFile.isEmpty()) {
@@ -872,6 +869,15 @@ bool Device::isEncryptedCleartext() const
     }
 }
 
+bool Device::isRoot() const
+{
+    if (isStorageAccess()) {
+        const UDisks2::StorageAccess accessIface(const_cast<Device *>(this));
+        return accessIface.filePath() == QLatin1String("/");
+    }
+    return false;
+}
+
 bool Device::isSwap() const
 {
     return hasInterface(QStringLiteral(UD2_DBUS_INTERFACE_SWAP));

src/solid/devices/backends/udisks2/udisksdevice.h

@@ -81,6 +81,7 @@ public:
     bool isMounted() const;
     bool isEncryptedContainer() const;
     bool isEncryptedCleartext() const;
+    bool isRoot() const;
     bool isSwap() const;
     bool isLoop() const;