Backend: blacklist blockstream electrum servers

Blockstream electrum servers don't support sending verbose
transactions (see [1]), and we use this functionality to get
confirmations of a transaction; so we prevent a crash by
blacklisting them.

[1] Blockstream/electrs#36

src/GWallet.Backend/Server.fs

@@ -173,6 +173,11 @@ module ServerRegistry =
             // they create exception when being queried for advanced ones (e.g. latest block)
                 server.ServerInfo.NetworkPath.Contains "blockscout" ||
 
+                // Blockstream electrum servers doesn't support sending verbose transactions, we use this functionality
+                // for getting confirmations of a transaction, this causes geewallet to crash. See:
+                // https://github.com/Blockstream/electrs/pull/36
+                server.ServerInfo.NetworkPath.Contains "blockstream" ||
+
             // there was a mistake when adding this server to geewallet's JSON: it was added in the ETC currency instead of ETH
                 (currency = Currency.ETC && server.ServerInfo.NetworkPath.Contains "ethrpc.mewapi.io")