Don't read from disk when checking volume type

Should be faster than relying on the OS to cache the magic words.
Also gets rid of the odd recursive call in VolumeDirectory.

Source/Core/DolphinWX/ISOFile.cpp

@@ -62,14 +62,14 @@ GameListItem::GameListItem(const std::string& _rFileName)
 
 		if (pVolume != nullptr)
 		{
-			if (!DiscIO::IsVolumeWadFile(pVolume))
-				m_Platform = DiscIO::IsVolumeWiiDisc(pVolume) ? WII_DISC : GAMECUBE_DISC;
+			if (!pVolume->IsWadFile())
+				m_Platform = pVolume->IsWiiDisc() ? WII_DISC : GAMECUBE_DISC;
 			else
 				m_Platform = WII_WAD;
 
 			m_volume_names = pVolume->GetNames();
 
-			m_Country  = pVolume->GetCountry();
+			m_Country = pVolume->GetCountry();
 			m_FileSize = pVolume->GetRawSize();
 			m_VolumeSize = pVolume->GetSize();
 
@@ -281,7 +281,7 @@ const std::string GameListItem::GetWiiFSPath() const
 	if (iso == nullptr)
 		return ret;
 
-	if (DiscIO::IsVolumeWiiDisc(iso) || DiscIO::IsVolumeWadFile(iso))
+	if (iso->IsWiiDisc() || iso->IsWadFile())
 	{
 		u64 title = 0;