Handle `JsonRpcError` in `_estimate_fee_basic`

[kristapsk]

_estimate_fee_basic is supposed to return None if fee rate can't be estimated and then estimate_fee_per_kb handles that with hardcoded fallback fee. But JsonRpcError wasn't handled and it could fail when fee estimation is not working in Core.

Fixes #1653.

Previously it outputed unhandled error and hanged, now it's:

2024-02-10 02:05:11,803 [DEBUG]  rpc: estimatesmartfee [3]
2024-02-10 02:05:11,812 [WARNING]  Could not source a fee estimate from Core
2024-02-10 02:05:11,813 [WARNING]  Fee estimation for 3 block confirmation target failed. Falling back to default (randomized for privacy): 11976 sat/kvB (11.9 sat/vB).
2024-02-10 02:05:11,815 [DEBUG]  rpc: getmempoolinfo []
2024-02-10 02:05:11,818 [DEBUG]  rpc: estimatesmartfee [3]
2024-02-10 02:05:11,820 [WARNING]  Could not source a fee estimate from Core
2024-02-10 02:05:11,821 [WARNING]  Fee estimation for 3 block confirmation target failed. Falling back to default (randomized for privacy): 10279 sat/kvB (10.2 sat/vB).
2024-02-10 02:05:11,849 [INFO]  Using a fee of: 0.00001449 BTC (1449 sat).