Set last header flag in FLAC Metadata block type field

In case the Vorbis comment block is the last one the last block flag
has to be set.

As the other metadata blocks are kept as is, and in original order,
and no other metadata blocks are added/inserted, these can be kept
as is.

Also warn if the header scan loop detects a frame sync sequence (which
is the head of the first non-header packet). Previously, this was
detected as the last header packet, but streamStart and streamLength
are unused, and all packets but the vorbis comment packet are just copied
in order.

See taglib#1297

Author: StefanBruens

taglib/ogg/flac/oggflacfile.cpp

@@ -46,6 +46,7 @@ class Ogg::FLAC::File::FilePrivate
 
   bool hasXiphComment { false };
   int commentPacket { 0 };
+  int lastHeaderPacket { 0 };
 };
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -129,6 +130,12 @@ bool Ogg::FLAC::File::save()
 
   v[0] = 4;
 
+  // If the comment block is the last one, set the corresponding bit
+
+  if (d->commentPacket == d->lastHeaderPacket) {
+    v[0] = static_cast<char>(0x84);
+  }
+
   // Append the comment-data after the 32 bit header
 
   v.append(d->xiphCommentData);
@@ -282,6 +289,12 @@ void Ogg::FLAC::File::scan()
       return;
     }
 
+    if(((header[0] & 0xff) == 0xff) && ((header[1] & 0xff) == 0xf8)) {
+      ipacket--;
+      debug("Ogg::FLAC::File::scan() -- Found frame sync marker, possibly missing last block marker");
+      break;
+    }
+
     blockType = header[0] & 0x7f;
     lastBlock = (header[0] & 0x80) != 0;
     length = header.toUInt(1, 3, true);
@@ -315,6 +328,7 @@ void Ogg::FLAC::File::scan()
       debug("Ogg::FLAC::File::scan() -- Unknown metadata block");
     }
   }
+  d->lastHeaderPacket = ipacket;
 
   // End of metadata, now comes the datastream
   d->streamStart = overhead;