fix(JitsiConference): decline P2P offer if should not be in P2P

The client will reject P2P session-initiate if the conditions which
allow for P2P session to start are not met(there more or less than 2
human participants in the call).

JitsiConference.js

     ACTION_JINGLE_SI_RECEIVED,
     ACTION_JINGLE_SI_TIMEOUT,
     ACTION_JINGLE_TERMINATE,
+    ACTION_P2P_DECLINED,
     ACTION_P2P_ESTABLISHED,
     ACTION_P2P_FAILED,
     ACTION_P2P_SWITCH_TO_JVB,
             reasonDescription: 'P2P already in progress',
             errorMsg: 'Duplicated P2P "session-initiate"'
         };
+    } else if (!this._shouldBeInP2PMode()) {
+        rejectReason = {
+            reason: 'decline',
+            reasonDescription: 'P2P requirements not met',
+            errorMsg: 'Received P2P "session-initiate" when should not be in P2P mode'
+        };
+        Statistics.sendAnalytics(createJingleEvent(ACTION_P2P_DECLINED));
     }
 
     if (rejectReason) {
     }
     const peers = this.getParticipants();
     const peerCount = peers.length;
-    const hasBotPeer
-        = peers.find(p => p._botType === 'poltergeist') !== undefined;
 
     // FIXME 1 peer and it must *support* P2P switching
-    const shouldBeInP2P = peerCount === 1 && !hasBotPeer;
-
-    logger.debug(`P2P? peerCount: ${peerCount}, hasBotPeer: ${hasBotPeer} => ${shouldBeInP2P}`);
+    const shouldBeInP2P = this._shouldBeInP2PMode();
 
     // Clear deferred "start P2P" task
     if (!shouldBeInP2P && this.deferredStartP2PTask) {
     }
 };
 
+/**
+ * Tells whether or not this conference should be currently in the P2P mode.
+ *
+ * @private
+ * @returns {boolean}
+ */
+JitsiConference.prototype._shouldBeInP2PMode = function() {
+    const peers = this.getParticipants();
+    const peerCount = peers.length;
+    const hasBotPeer = peers.find(p => p._botType === 'poltergeist') !== undefined;
+    const shouldBeInP2P = peerCount === 1 && !hasBotPeer;
+
+    logger.debug(`P2P? peerCount: ${peerCount}, hasBotPeer: ${hasBotPeer} => ${shouldBeInP2P}`);
+
+    return shouldBeInP2P;
+};
+
 /**
  * Stops the current P2P session.
  * @param {string} [reason="success"] one of the Jingle "reason" element

modules/xmpp/JingleSessionPC.js

         this.state = JingleSessionState.ENDED;
         this.establishmentDuration = undefined;
 
-        this.peerconnection.onicecandidate = null;
-        this.peerconnection.oniceconnectionstatechange = null;
-        this.peerconnection.onnegotiationneeded = null;
-        this.peerconnection.onsignalingstatechange = null;
+        if (this.peerconnection) {
+            this.peerconnection.onicecandidate = null;
+            this.peerconnection.oniceconnectionstatechange = null;
+            this.peerconnection.onnegotiationneeded = null;
+            this.peerconnection.onsignalingstatechange = null;
+        }
 
         // Remove any pending tasks from the queue
         this.modificationQueue.clear();

service/statistics/AnalyticsEvents.js

 export const ACTION_JINGLE_TR_SUCCESS
     = 'transport-replace.success';
 
+/**
+ * The "action" value for P2P events which indicates that P2P session initiate message has been rejected by the client
+ * because the mandatory requirements were not met.
+ * @type {string}
+ */
+export const ACTION_P2P_DECLINED = 'decline';
+
 /**
  * The "action" value for P2P events which indicates that a connection was
  * established (TODO: verify/fix the documentation)