force new headers download if file is corrupted

lib/blockchain.py

@@ -258,7 +258,7 @@ class Blockchain(util.PrintError):
         return deserialize_header(h, height)
 
     def get_hash(self, height):
-        return bitcoin.GENESIS if height == 0 else hash_header(self.read_header(height))
+        return hash_header(self.read_header(height))
 
     def BIP9(self, height, flag):
         v = self.read_header(height)['version']

lib/network.py

@@ -946,10 +946,11 @@ class Network(util.DaemonThread):
             self.process_responses(interface)
 
     def init_headers_file(self):
-        filename = self.blockchains[0].path()
-        if os.path.exists(filename):
+        b = self.blockchains[0]
+        if b.get_hash(0) == bitcoin.GENESIS:
             self.downloading_headers = False
             return
+        filename = b.path()
         def download_thread():
             try:
                 import urllib, socket