LN invoice: better handle unknown required featured bits in bolt11 invs

A user provided an invoice that requires feature bit 30. (That bit is not in the spec)
To test:
```
lnbc1p324a66pp5tundykxx3q5kztsr8x00eknpn2uwe3394cnky3j9a0fswm568wnsdp9facx2mj5d9kk2um5v9khqueqv3hkuct5d9hkucqzpgxq9z0rgqsp5l73jgfgctzc92juer5rk2mqcrkj8teng53dr9vfxj4n8lulu4jmq9q8pqqqssq4gacn859tpzz99hkusnh7m93d5ncpx3t4zns8ynca7akmljpl5vh504qjz7dqwewqjh4md7xagaz5wg85knvxywrhp0sp2t09yta7lcq3qs6fy

lntb1p324a66pp5tundykxx3q5kztsr8x00eknpn2uwe3394cnky3j9a0fswm568wnssp5l73jgfgctzc92juer5rk2mqcrkj8teng53dr9vfxj4n8lulu4jmqdp9facx2mj5d9kk2um5v9khqueqv3hkuct5d9hkuxq9z0rgq9q8pqqqssqdte0z9dy7ur7fagsk7r3mtfj6upq88xfylhufys87zqpamklcfgn2f3xeq3nlhvn3qy9tdgg42vq9eq99qz6rz6tzqezfhzuv6zsr5qp7cgel4
```

electrum/gui/qt/send_tab.py

@@ -12,6 +12,7 @@ from PyQt5.QtWidgets import (QLabel, QVBoxLayout, QGridLayout,
                              QHBoxLayout, QCompleter, QWidget, QToolTip)
 
 from electrum import util, paymentrequest
+from electrum import lnutil
 from electrum.plugin import run_hook
 from electrum.i18n import _
 from electrum.util import (get_asyncio_loop, bh2u,
@@ -402,6 +403,9 @@ class SendTab(QWidget, MessageBoxMixin, Logger):
         except LnInvoiceException as e:
             self.show_error(_("Error parsing Lightning invoice") + f":\n{e}")
             return
+        except lnutil.IncompatibleOrInsaneFeatures as e:
+            self.show_error(_("Invoice requires unknown or incompatible Lightning feature") + f":\n{e!r}")
+            return
 
         pubkey = bh2u(lnaddr.pubkey.serialize())
         for k,v in lnaddr.tags: