wallet: properly calculate confirmations in GetTransaction

Fix bug where GetTransaction was setting confirmations to the
block height instead of calculating them correctly. The formula
should be: `confirmations = currentHeight - txBlockHeight + 1`

Author: mohamedawnallah

wallet/wallet.go

@@ -2597,14 +2597,18 @@ func (w *Wallet) GetTransaction(txHash chainhash.Hash) (*GetTransactionResult,
 		res = GetTransactionResult{
 			Summary:       makeTxSummary(dbtx, w, txDetail),
 			Timestamp:     txDetail.Block.Time.Unix(),
-			Confirmations: txDetail.Block.Height,
+			Confirmations: 0,
 		}
 
 		// If it is a confirmed transaction we set the corresponding
 		// block height and hash.
 		if txDetail.Block.Height != -1 {
 			res.Height = txDetail.Block.Height
 			res.BlockHash = &txDetail.Block.Hash
+
+			bestBlock := w.SyncedTo()
+			blockHeight := txDetail.Block.Height
+			res.Confirmations = bestBlock.Height - blockHeight + 1
 		}
 
 		return nil