Fix lightwalletd sync loop for DragonX wallet

- Handle missing Sapling upgrade in getblockchaininfo response by
  defaulting activation height to 1 (DragonX has Sapling active from
  genesis but uses NO_ACTIVATION_HEIGHT in chainparams)
- Override consensus branch ID to Sapling (76b809bb) when node reports
  Sprout (00000000) due to disabled activation heights
- Include full serialized block header in CompactBlock so the SDK can
  validate hashFinalSaplingRoot against the Sapling commitment tree
- Set CompactBlock ProtoVersion to 1

parser/block.go

@@ -99,12 +99,14 @@ func (b *Block) GetPrevHash() []byte {
 }
 
 func (b *Block) ToCompact() *walletrpc.CompactBlock {
+	headerBytes, _ := b.hdr.MarshalBinary()
 	compactBlock := &walletrpc.CompactBlock{
-		//TODO ProtoVersion: 1,
-		Height:   uint64(b.GetHeight()),
-		PrevHash: b.hdr.HashPrevBlock,
-		Hash:     b.GetEncodableHash(),
-		Time:     b.hdr.Time,
+		ProtoVersion: 1,
+		Height:       uint64(b.GetHeight()),
+		PrevHash:     b.hdr.HashPrevBlock,
+		Hash:         b.GetEncodableHash(),
+		Time:         b.hdr.Time,
+		Header:       headerBytes,
 	}
 
 	// Only Sapling transactions have a meaningful compact encoding