Defer heartbeat during resume

Hotfix for #921 and discord / discord-api-docs # 1619 until they deploy that

lib/gateway/Shard.js

@@ -1372,6 +1372,9 @@ class Shard extends EventEmitter {
                 this.client.shards._readyPacketCB();
 
                 if(packet.t === "RESUMED") {
+                    // Can only heartbeat after resume succeeds, discord/discord-api-docs#1619
+                    this.heartbeat();
+
                     this.preReady = true;
                     this.ready = true;
 
@@ -1934,8 +1937,9 @@ class Shard extends EventEmitter {
                     this.resume();
                 } else {
                     this.identify();
+                    // Cannot heartbeat when resuming, discord/discord-api-docs#1619
+                    this.heartbeat();
                 }
-                this.heartbeat();
                 /**
                 * Fired when a shard receives an OP:10/HELLO packet
                 * @event Client#hello
@@ -1959,6 +1963,10 @@ class Shard extends EventEmitter {
     }
 
     heartbeat(normal) {
+        // Can only heartbeat after resume succeeds, discord/discord-api-docs#1619
+        if(this.status === "resuming") {
+            return;
+        }
         if(normal) {
             if(!this.lastHeartbeatAck) {
                 this.emit("debug", "Heartbeat timeout; " + JSON.stringify({