{standard} Always write a CV index packet

This is required by the standard.

9.3.5: "A CompressedVector shall contain at least one index packet and at least one data packet."

To satisfy this requirement, we write one index packet containing one entry which points to the first data packet.

src/CompressedVectorWriterImpl.cpp

@@ -183,6 +183,9 @@ namespace e57
          flush();
       }
 
+      // Write one index packet (required by standard).
+      packetWriteIndex();
+
       // Compute length of whole section we just wrote (from section start to
       // current start of free space).
       sectionLogicalLength_ = imf->unusedLogicalStart_ - sectionHeaderLogicalStart_;
@@ -660,6 +663,31 @@ namespace e57
       dataPacketsCount_++;
    }
 
+   // Write one index packet.
+   // We don't have an interface to work with index packets, but one is required by the standard, so
+   // write one index packet with one entry pointing to the first data packet.
+   void e57::CompressedVectorWriterImpl::packetWriteIndex()
+   {
+      ImageFileImplSharedPtr imf( cVector_->destImageFile_ );
+
+      IndexPacket indexPacket;
+
+      indexPacket.entries[0].chunkPhysicalOffset = dataPhysicalOffset_;
+
+      const auto cPacketLength = sizeof( IndexPacketHeader ) + sizeof( IndexPacket::Entry );
+
+      indexPacket.header.packetLogicalLengthMinus1 = cPacketLength - 1;
+      indexPacket.header.entryCount = 1;
+
+      uint64_t packetLogicalOffset = imf->allocateSpace( cPacketLength, false );
+      topIndexPhysicalOffset_ = imf->file_->logicalToPhysical( packetLogicalOffset );
+
+      imf->file_->seek( packetLogicalOffset );
+      imf->file_->write( reinterpret_cast<const char *>( &indexPacket ), cPacketLength );
+
+      indexPacketsCount_++;
+   }
+
    void CompressedVectorWriterImpl::flush()
    {
       for ( auto &bytestream : bytestreams_ )

src/CompressedVectorWriterImpl.h

@@ -58,6 +58,7 @@ namespace e57
       size_t currentPacketSize() const;
       uint64_t packetWrite();
       void packetWriteZeroRecords();
+      void packetWriteIndex();
 
       void flush();