Reduce indentation level

This makes the method easier to read.
Skip negative tx heights too. A transaction height can be negative too, see the
wallet modules TX_HEIGHT_LOCAL and TX_HEIGHT_UNCONF_PARENT constants.

lib/verifier.py

@@ -42,23 +42,25 @@ class SPV(ThreadJob):
         interface = self.network.interface
         if not interface:
             return
+
         blockchain = interface.blockchain
         if not blockchain:
             return
-        lh = self.network.get_local_height()
+
+        local_height = self.network.get_local_height()
         unverified = self.wallet.get_unverified_txs()
         for tx_hash, tx_height in unverified.items():
             # do not request merkle branch before headers are available
-            if (tx_height > 0) and (tx_height <= lh):
+            if tx_height <= 0 or tx_height > local_height:
+                continue
+
             header = blockchain.read_header(tx_height)
             if header is None:
                 index = tx_height // 2016
                 if index < len(blockchain.checkpoints):
                     self.network.request_chunk(interface, index)
-                else:
+            elif (tx_hash not in self.requested_merkle
-                    if (tx_hash not in self.requested_merkle
                     and tx_hash not in self.merkle_roots):
-
                 self.network.get_merkle_for_transaction(
                         tx_hash,
                         tx_height,