If a drive isn't ready, don't try to mount it at all; it may cause mkdir()

calls to be made (if eg. mounting "D:\foo"), causing "volume not ready"
dialogs.  This happens with removable devices like memory card readers
that don't have a device.

I think this is generally incorrect: if a user has a memcard reader, we'll ignore
it on the first change (no device is installed), and then we'll never actually
notice when a card is inserted, since the drive letters don't actually
change.  I don't have a memcard reader to test this, so I'm punting on
this for now.

stepmania/src/arch/MemoryCard/MemoryCardDriverThreaded_Windows.cpp

@@ -19,7 +19,7 @@ MemoryCardDriverThreaded_Windows::MemoryCardDriverThreaded_Windows()
 
 typedef const CString& CCStringRef;
 
-bool TestWrite( CCStringRef sDrive )
+static bool TestReady( CCStringRef sDrive )
 {
 	// TODO: Use RageFileDirect here to detect ready state?
 	TCHAR szVolumeNameBuffer[MAX_PATH];
@@ -27,7 +27,8 @@ bool TestWrite( CCStringRef sDrive )
 	DWORD dwMaximumComponentLength;
 	DWORD lpFileSystemFlags;
 	TCHAR szFileSystemNameBuffer[MAX_PATH];
-	BOOL bReady = GetVolumeInformation( 
+
+	return !!GetVolumeInformation( 
 		sDrive,
 		szVolumeNameBuffer,
 		sizeof(szVolumeNameBuffer),
@@ -36,9 +37,10 @@ bool TestWrite( CCStringRef sDrive )
 		&lpFileSystemFlags,
 		szFileSystemNameBuffer,
 		sizeof(szFileSystemNameBuffer) );
-	if( !bReady )
+}
-		return false;
 
+static bool TestWrite( CCStringRef sDrive )
+{
 	// Try to write a file.
 	// TODO: Can we use RageFile for this?
 	CString sFile = sDrive + "temp";
@@ -72,8 +74,12 @@ void MemoryCardDriverThreaded_Windows::MountThreadMain()
 
 					LOG->Trace( "Found drive %s", sDrive.c_str() );
 
-					if( GetDriveType(sDrive) == DRIVE_REMOVABLE )	// is a removable drive
+					if( GetDriveType(sDrive) != DRIVE_REMOVABLE )	// is a removable drive
-					{
+						continue;
+
+					if( !TestReady(sDrive) )
+						continue;
+
 					UsbStorageDeviceEx usbd;
 					usbd.sOsMountDir = sDrive;
 					usbd.bWriteTestSucceeded = TestWrite( sDrive );
@@ -89,7 +95,6 @@ void MemoryCardDriverThreaded_Windows::MountThreadMain()
 					vNewStorageDevices.push_back( usbd );
 				}
 			}
-			}
 
 			{
 				LockMut( m_mutexStorageDevices );