Check login flows only if MSC4190 is not enabled (#178)

Currently, the homeserver login flows are checked even if MSC4190 is
enabled. However, the `flows` variable is unused when MSC4190 is
enabled.

This is an unnecessary network call, and also e.g. requires a
reverse proxy soley for this purpose if bridges would otherwise
directly connect to a homeserver that is delegating OIDC authentication.

Closes #177.

Author: meson800

mautrix/bridge/e2ee.py

@@ -247,12 +247,13 @@ async def decrypt(self, evt: EncryptedEvent, wait_session_timeout: int = 5) -> M
         return decrypted
 
     async def start(self) -> None:
-        flows = await self.client.get_login_flows()
-        if not self.msc4190 and not flows.supports_type(LoginType.APPSERVICE):
-            self.log.critical(
-                "Encryption enabled in config, but homeserver does not support appservice login"
-            )
-            sys.exit(30)
+        if not self.msc4190:
+            flows = await self.client.get_login_flows()
+            if not flows.supports_type(LoginType.APPSERVICE):
+                self.log.critical(
+                    "Encryption enabled in config, but homeserver does not support appservice login"
+                )
+                sys.exit(30)
         self.log.debug("Logging in with bridge bot user")
         if self.crypto_db:
             try: