contrib: fix eof not detected when looking for an ID size

do use the data in memory that wasn't actually read

Close #14783
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/ebml/eof.patch

+--- libebml/src/EbmlElement.cpp 2015-08-21 12:58:03.738589700 +0200
++++ libebml/src/EbmlElement.cpp.eof     2015-08-21 12:55:18.972736500 +0200
+@@ -417,7 +417,10 @@
+         bFound = false;
+         break;
+       }
+-      ReadSize += DataStream.read(&PossibleIdNSize[SizeIdx++], 1);
++      if( DataStream.read( &PossibleIdNSize[SizeIdx++], 1 ) == 0 ) {
++          return NULL; // no more data ?
++      }
++      ReadSize++;
+       PossibleSizeLength++;
+     }
+
+

contrib/src/ebml/rules.mak

@@ -11,6 +11,7 @@ $(TARBALLS)/libebml-$(EBML_VERSION).tar.bz2:
 
 libebml: libebml-$(EBML_VERSION).tar.bz2 .sum-ebml
 	$(UNPACK)
+	$(APPLY) $(SRC)/ebml/eof.patch
 	$(MOVE)
 
 # libebml requires exceptions