Bugfix crash on unexpected error from gettransaction call.

Prior to this commit, if the call to the bitcoin rpc
gettransaction resulted in an exception other than JsonRpcError,
the code would crash as the variable `res` was uninitialized.
This fixes that by always setting res to None in this case, and
also promotes the logging messages for such errors to warning.

jmclient/jmclient/blockchaininterface.py

@@ -306,7 +306,7 @@ class ElectrumWalletInterface(BlockchainInterface): #pragma: no cover
 
     def estimate_fee_per_kb(self, N):
         if super(ElectrumWalletInterface, self).fee_per_kb_has_been_manually_set(N):
-	     # use a floor of 1000 to not run into node relay problems
+            # use a floor of 1000 to not run into node relay problems
             return int(max(1000, random.uniform(N * float(0.8), N * float(1.2))))
         fee = self.wallet.network.synchronous_get(('blockchain.estimatefee', [N]
                                                   ))
@@ -688,10 +688,12 @@ class BitcoinCoreInterface(BlockchainInterface):
                     res = self.rpc("gettransaction", [tx["txid"], 1])
                 except JsonRpcError as e:
                     #This should never happen (gettransaction is a wallet rpc).
-                    log.info("Failed any gettransaction call")
+                    log.warn("Failed gettransaction call; JsonRpcError")
                     res = None
                 except Exception as e:
-                    log.info(str(e))
+                    log.warn("Failed gettransaction call; unexpected error:")
+                    log.warn(str(e))
+                    res = None
             if not res:
                 continue
             if "confirmations" not in res: