Fix switch failed start (#770)

libp2p/switch.nim

@@ -312,12 +312,10 @@ proc start*(s: Switch) {.async, gcsafe, public.} =
 
   await allFutures(startFuts)
 
-  for s in startFuts:
-    if s.failed:
-      # TODO: replace this exception with a `listenError` callback. See
-      # https://github.com/status-im/nim-libp2p/pull/662 for more info.
-      raise newException(transport.TransportError,
-        "Failed to start one transport", s.error)
+  for fut in startFuts:
+    if fut.failed:
+      await s.stop()
+      raise fut.error
 
   for t in s.transports: # for each transport
     if t.addrs.len > 0 or t.running:

tests/testswitch.nim

@@ -1035,3 +1035,12 @@ suite "Switch":
     await conn.close()
     await src.stop()
     await dst.stop()
+
+  asyncTest "switch failing to start stops properly":
+    let switch = newStandardSwitch(
+      addrs = @[MultiAddress.init("/ip4/0.0.0.0/tcp/0").tryGet(), MultiAddress.init("/ip4/1.1.1.1/tcp/0").tryGet()]
+    )
+
+    expect LPError:
+      await switch.start()
+    # test is that this doesn't leak