Don't serve requests until startup complete (#498)

* Don't serve requests until startup complete

* Send lifespan shutdown on socket bind exception

* Black formatter

uvicorn/main.py

@@ -411,6 +411,11 @@ async def serve(self, sockets=None):
         )
 
     async def startup(self, sockets=None):
+        await self.lifespan.startup()
+        if self.lifespan.should_exit:
+            self.should_exit = True
+            return
+
         config = self.config
 
         create_protocol = functools.partial(
@@ -464,6 +469,7 @@ async def startup(self, sockets=None):
                 )
             except OSError as exc:
                 logger.error(exc)
+                await self.lifespan.shutdown()
                 sys.exit(1)
             port = config.port
             if port == 0:
@@ -484,11 +490,7 @@ async def startup(self, sockets=None):
             )
             self.servers = [server]
 
-        await self.lifespan.startup()
-        if self.lifespan.should_exit:
-            self.should_exit = True
-        else:
-            self.started = True
+        self.started = True
 
     async def main_loop(self):
         counter = 0