Simplify event resolving logic

Although this commit introduces a race condition since an
event may only be half-resolved. A lock is thus needed,
but it depends on an event-loop to which we don't have
access in the class-level.

telethon/events/common.py

@@ -57,7 +57,7 @@ class EventBuilder(abc.ABC):
     def __init__(self, chats=None, blacklist_chats=False):
         self.chats = chats
         self.blacklist_chats = blacklist_chats
-        self._self_id = None
+        self.resolved = False
 
     @classmethod
     @abc.abstractmethod
@@ -66,9 +66,11 @@ class EventBuilder(abc.ABC):
 
     async def resolve(self, client):
         """Helper method to allow event builders to be resolved before usage"""
-        self.chats = await _into_id_set(client, self.chats)
-        if not EventBuilder.self_id:
-            EventBuilder.self_id = await client.get_peer_id('me')
+        if not self.resolved:
+            self.resolved = True
+            self.chats = await _into_id_set(client, self.chats)
+            if not EventBuilder.self_id:
+                EventBuilder.self_id = await client.get_peer_id('me')
 
     def filter(self, event):
         """

telethon/events/newmessage.py

@@ -71,8 +71,9 @@ class NewMessage(EventBuilder):
         ))
 
     async def resolve(self, client):
-        await super().resolve(client)
-        self.from_users = await _into_id_set(client, self.from_users)
+        if not self.resolved:
+            await super().resolve(client)
+            self.from_users = await _into_id_set(client, self.from_users)
 
     @classmethod
     def build(cls, update):

telethon/events/raw.py

@@ -27,7 +27,7 @@ class Raw(EventBuilder):
             self.types = tuple(types)
 
     async def resolve(self, client):
-        pass
+        self.resolved = True
 
     @classmethod
     def build(cls, update):