decklink: Fix issues showing older devices

Certain older devices (such as the Decklink Duo and Quad) could not be
selected due to the fact that they rely on BMDDeckLinkTopologicalID for
their unique identifier rather than BMDDeckLinkPersistentID.

See http://forum.blackmagicdesign.com/viewtopic.php?f=12&t=33967

Closes jp9000/obs-studio#517

plugins/decklink/decklink-device.cpp

@@ -72,8 +72,13 @@ bool DeckLinkDevice::Init()
 	if (result != S_OK)
 		return true;
 
+	/* http://forum.blackmagicdesign.com/viewtopic.php?f=12&t=33967
+	 * BMDDeckLinkTopologicalID for older devices
+	 * BMDDeckLinkPersistentID for newer ones */
+
 	int64_t value;
-	if (attributes->GetInt(BMDDeckLinkPersistentID, &value) != S_OK)
+	if (attributes->GetInt(BMDDeckLinkPersistentID,  &value) != S_OK &&
+	    attributes->GetInt(BMDDeckLinkTopologicalID, &value) != S_OK)
 		return true;
 
 	std::ostringstream os;