test: fund wallet before testing fundchannel

After switching to a plugin, we verify that we can fund a channel
before we check to contact a peer. We'll need to have a funded wallet
to pass the check in this test that verifies that 'fundchannel' cannot
be called for a peer after fundchannel_start is.

tests/test_connection.py

@@ -851,6 +851,8 @@ def test_funding_external_wallet_corners(node_factory, bitcoind):
     l2 = node_factory.get_node()
 
     amount = 2**24
+    l1.fundwallet(amount + 10000000)
+
     # Fail to open (too large)
     with pytest.raises(RpcError, match=r'Amount exceeded 16777215'):
         l1.rpc.fundchannel_start(l2.info['id'], amount)