Merge pull request #30 from Matroska-Org/enc-algo-mandatory

fix ContentEncAlgo assumed not to be mandatory

diff --cc src/KaxSemantic.cpp
index 6567c2ab12204aef579c9043dd1d1658ac5b36e6,061fd148c4bc07014e531c4afe548847f29b7918..7ce5ee0622d184de1b60606f1857032672b52e56
--- 1/src/KaxSemantic.cpp
--- 2/src/KaxSemantic.cpp
+++ b/src/KaxSemantic.cpp
@@@ -501,9 -547,8 +501,9 @@@ DEFINE_MKX_UINTEGER_DEF(KaxContentCompA
  DEFINE_MKX_BINARY (KaxContentCompSettings, 0x4255, 2, KaxContentCompression, "ContentCompSettings")
  
  DEFINE_START_SEMANTIC(KaxContentEncryption)
- DEFINE_SEMANTIC_ITEM(false, true, KaxContentEncAlgo)
+ DEFINE_SEMANTIC_ITEM(true, true, KaxContentEncAlgo)
  DEFINE_SEMANTIC_ITEM(false, true, KaxContentEncKeyID)
 +DEFINE_SEMANTIC_ITEM(false, true, KaxContentEncAESSettings)
  DEFINE_SEMANTIC_ITEM(false, true, KaxContentSignature)
  DEFINE_SEMANTIC_ITEM(false, true, KaxContentSigKeyID)
  DEFINE_SEMANTIC_ITEM(false, true, KaxContentSigAlgo)