Add link connected property

bumble/device.py

@@ -1447,6 +1447,10 @@ async def disconnect(
     ) -> None:
         await self.device.disconnect(self, reason)
 
+    @property
+    def is_connected(self) -> bool:
+        return self in self.device.sco_links.values()
+
 
 # -----------------------------------------------------------------------------
 class _IsoLink:
@@ -1644,6 +1648,10 @@ async def disconnect(
     ) -> None:
         await self.device.disconnect(self, reason)
 
+    @property
+    def is_connected(self) -> bool:
+        return self in self.device.cis_links.values()
+
 
 # -----------------------------------------------------------------------------
 @dataclass
@@ -1870,7 +1878,11 @@ def is_encrypted(self) -> bool:
 
     @property
     def is_incomplete(self) -> bool:
-        return self.handle is None
+        return self.handle == 0
+
+    @property
+    def is_connected(self) -> bool:
+        return self in self.device.connections.values()
 
     def send_l2cap_pdu(self, cid: int, pdu: bytes) -> None:
         self.device.send_l2cap_pdu(self.handle, cid, pdu)
@@ -1913,6 +1925,8 @@ async def switch_role(self, role: hci.Role) -> None:
 
     async def sustain(self, timeout: Optional[float] = None) -> None:
         """Idles the current task waiting for a disconnect or timeout"""
+        if not self.is_connected:
+            return
 
         abort = asyncio.get_running_loop().create_future()
         self.on(self.EVENT_DISCONNECTION, abort.set_result)