fix(dash): preserve MPD DRM instead of overwriting from init segment

The init_data DRM extraction was unconditionally overwriting DRM already extracted from MPD ContentProtection elements. This caused failures when init segments contain malformed PSSH data while the MPD has valid PSSH.

Now only falls back to init_data extraction when no DRM was found from the manifest, matching the behavior in version 2.1.0.

unshackle/core/manifests/dash.py

@@ -476,7 +476,7 @@ class DASH:
         track.data["dash"]["timescale"] = int(segment_timescale)
         track.data["dash"]["segment_durations"] = segment_durations
 
-        if init_data and isinstance(track, (Video, Audio)):
+        if not track.drm and init_data and isinstance(track, (Video, Audio)):
             prefers_playready = isinstance(cdm, PlayReadyCdm) or (hasattr(cdm, "is_playready") and cdm.is_playready)
             if prefers_playready:
                 try:
@@ -866,7 +866,7 @@ class DASH:
             urn = (protection.get("schemeIdUri") or "").lower()
 
             if urn == WidevineCdm.urn:
-                pssh_text = protection.findtext("pssh")
+                pssh_text = protection.findtext("pssh") or protection.findtext("{urn:mpeg:cenc:2013}pssh")
                 if not pssh_text:
                     continue
                 pssh = PSSH(pssh_text)
@@ -897,6 +897,7 @@ class DASH:
             elif urn in ("urn:uuid:9a04f079-9840-4286-ab92-e65be0885f95", "urn:microsoft:playready"):
                 pr_pssh_b64 = (
                     protection.findtext("pssh")
+                    or protection.findtext("{urn:mpeg:cenc:2013}pssh")
                     or protection.findtext("pro")
                     or protection.findtext("{urn:microsoft:playready}pro")
                 )