Abandon fetching offline presence on 400 error

It seems like some servers return a M_UNRECOGNIZED code instead of
M_FORBIDDEN or "offline" when trying to fetch the presence for a user
and it's not available.

Fixes https://github.com/mirukana/mirage/issues/116

src/backend/errors.py

@@ -33,6 +33,12 @@ class MatrixError(Exception):
         return cls(response.transport_response.status, response.status_code)
 
 
+@dataclass
+class MatrixUnrecognized(MatrixError):
+    http_code: int = 400
+    m_code:    str = "M_UNRECOGNIZED"
+
+
 @dataclass
 class MatrixInvalidAccessToken(MatrixError):
     http_code: int = 401

src/backend/matrix_client.py

@@ -37,7 +37,7 @@ from . import __app_name__, __display_name__, utils
 from .errors import (
     BadMimeType, InvalidUserId, InvalidUserInContext, MatrixBadGateway,
     MatrixError, MatrixForbidden, MatrixInvalidAccessToken, MatrixNotFound,
-    MatrixTooLarge, MatrixUnauthorized, UneededThumbnail,
+    MatrixTooLarge, MatrixUnauthorized, MatrixUnrecognized, UneededThumbnail,
     UserFromOtherServerDisallowed,
 )
 from .html_markdown import HTML_PROCESSOR as HTML
@@ -1474,7 +1474,7 @@ class MatrixClient(nio.AsyncClient):
         try:
             async with self.backend.concurrent_get_presence_limit:
                 resp = await self.get_presence(user_id)
-        except MatrixForbidden:
+        except (MatrixForbidden, MatrixUnrecognized):
             return
 
         await self.nio_callbacks.onPresenceEvent(nio.PresenceEvent(