Merge #13424: Consistently validate txid / blockhash length and encoding in rpc calls

5eb20f81d9 Consistently use ParseHashV to validate hash inputs in rpc (Ben Woosley)

Pull request description:

  ParseHashV validates the length and encoding of the string and throws
  an informative RPC error on failure, which is as good or better than
  these alternative calls.

  Note I switched ParseHashV to check string length first, because
  IsHex tests that the length is even, and an error like:
  "must be of length 64 (not 63, for X)" is much more informative than
  "must be hexadecimal string (not X)" in that case.

  Split from #13420

Tree-SHA512: f0786b41c0d7793ff76e4b2bb35547873070bbf7561d510029e8edb93f59176277efcd4d183b3185532ea69fc0bbbf3dbe9e19362e8017007ae9d51266cd78ae

test/functional/p2p_sendheaders.py

@@ -402,7 +402,7 @@ class SendHeadersTest(BitcoinTestFramework):
 
             block_time += 9
 
-            fork_point = self.nodes[0].getblock("%02x" % new_block_hashes[0])["previousblockhash"]
+            fork_point = self.nodes[0].getblock("%064x" % new_block_hashes[0])["previousblockhash"]
             fork_point = int(fork_point, 16)
 
             # Use getblocks/getdata