Failure to reject `open_channel` where funder cannot pay commitment fee

BOLT 2 [requires](https://github.com/lightning/bolts/blob/152897261850d93c4f4597f39cf22d7d22d6ede6/02-peer-protocol.md?plain=1#L871) the receiver of `open_channel` to fail the channel when the funder's amount cannot cover the initial commitment fee:

```
The receiving node MUST fail the channel if:
- the funder's amount for the initial commitment transaction is not sufficient for full [fee payment](03-transactions.md#fee-payment).
```

CLN [implements](https://github.com/ElementsProject/lightning/blob/78f4cd729e28353cd23c9a2c55f44cfa1281220d/common/initial_commit_tx.c#L140-L160) the rule, but too late. The channel isn't rejected until later in the flow, after receiving `funding_created`.

### Impact

A peer can set a `push_msat` for the channel that leaves insufficient funds to pay the initial commitment fees. CLN initially accepts such channels and responds with `accept_channel`, even though it will inevitably reject them one roundtrip later in the funding flow (after receiving `funding_created`). This is entirely a spec compliance issue.

### Reproduction

```python
@pytest.mark.openchannel('v1')
def test_open_channel_funder_cannot_afford_fee(node_factory, bitcoind):
"""A funder left short of the commitment fee must be rejected.

BOLT 2: the receiving node MUST fail the channel if the funder's amount for
the initial commitment transaction is not sufficient for full fee payment.
CLN only notices in initial_commit_tx(), after accept_channel has gone out.
"""
l1 = node_factory.get_node()

chain_hash = bytes.fromhex(bitcoind.rpc.getblockhash(0))[::-1]
# Use the node's own opening feerate, so we're inside its accepted range.
feerate = l1.rpc.feerates('perkw')['perkw']['opening']
funding_sat = 16777216

# The funder pays the commitment fee out of its own balance, so pushing the
# balance away leaves it with nothing to pay from.
push_msat = funding_sat * 1000

lconn, channel_type = raw_peer_connect(l1)
temp_chan_id = os.urandom(32)
send_open_channel(lconn, chain_hash, temp_chan_id, funding_sat,
push_msat, feerate, channel_type)

mtype = read_channel_reply(lconn)
assert mtype in (WIRE_WARNING, WIRE_ERROR), \
"funder left with {} sat to pay the commitment fee was not rejected (got msgtype {})".format(
funding_sat - push_msat // 1000, mtype)
```

If we continue to flow to `funding_created`, the `initial_commit_tx` check rejects the channel:

```
UNUSUAL 034f355b...-openingd-chan#1: Funder cannot afford fee on initial commitment transaction
```

### Suggested fix

Apply the same check that already exists in [`initial_commit_tx`](https://github.com/ElementsProject/lightning/blob/78f4cd729e28353cd23c9a2c55f44cfa1281220d/common/initial_commit_tx.c#L140-L160) immediately after receiving `accept_channel`.

### Discovery

Found while fuzzing the v1 funding protocol with [smite](https://github.com/lnfuzz/smite).