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

@@ -42,29 +42,31 @@ 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):
-                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:
-                    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,
-                                self.verify_merkle)
-                        self.print_error('requested merkle', tx_hash)
-                        self.requested_merkle.add(tx_hash)
+            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)
+            elif (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,
+                        self.verify_merkle)
+                self.print_error('requested merkle', tx_hash)
+                self.requested_merkle.add(tx_hash)
 
         if self.network.blockchain() != self.blockchain:
             self.blockchain = self.network.blockchain()