Merge pull request #309 from LadMartin/bugfix/Channel-Unchecked-Callbacks

Adds channel callbacks checking

include/amqpcpp/channelimpl.h

@@ -218,7 +218,7 @@ public:
         _readyCallback = callback;
 
         // direct call if channel is already ready
-        if (_state == state_ready) callback();
+        if (_state == state_ready && callback) callback();
     }
 
     /**

src/channelimpl.cpp

@@ -73,7 +73,10 @@ void ChannelImpl::onError(const ErrorCallback &callback)
 
     // if the channel is usable, all is ok
     if (usable()) return;
-    
+
+    // validity check
+    if (!callback) return;
+
     // is the channel closing down?
     if (_state == state_closing) return callback("Channel is closing down");