Fixed compilation issue due to recent changes in ChannelImpl

include/channelimpl.h

@@ -213,26 +213,7 @@ public:
      *
      *  @param  callback    the callback to execute
      */
-    void onError(const ErrorCallback &callback)
-    {
-        // store callback
-        _errorCallback = callback;
-
-        // if the channel is connected, all is ok
-        if (connected()) return;
-        
-        // is the channel closing down?
-        if (_state == state_closing) return callback("Channel is closing down");
-
-        // the channel is closed, but what is the connection doing?
-        if (_connection == nullptr) return callback("Channel is not linked to a connection");
-        
-        // if the connection is valid, this is a pure channel error
-        if (_connection->connected()) return callback("Channel is in an error state, but the connection is valid");
-        
-        // direct call if channel is already in error state
-        callback("Channel is in error state because no AMQP connection is available");
-    }
+    void onError(const ErrorCallback &callback);
 
     /**
      *  Pause deliveries on a channel

src/channelimpl.cpp

@@ -60,6 +60,35 @@ ChannelImpl::~ChannelImpl()
     if (_connection) _connection->remove(this);
 }
 
+/**
+ *  Callback that is called when an error occurs.
+ *
+ *  Only one error callback can be registered. Calling this function
+ *  multiple times will remove the old callback.
+ *
+ *  @param  callback    the callback to execute
+ */
+void ChannelImpl::onError(const ErrorCallback &callback)
+{
+    // store callback
+    _errorCallback = callback;
+
+    // if the channel is connected, all is ok
+    if (connected()) return;
+    
+    // is the channel closing down?
+    if (_state == state_closing) return callback("Channel is closing down");
+
+    // the channel is closed, but what is the connection doing?
+    if (_connection == nullptr) return callback("Channel is not linked to a connection");
+    
+    // if the connection is valid, this is a pure channel error
+    if (_connection->connected()) return callback("Channel is in an error state, but the connection is valid");
+    
+    // direct call if channel is already in error state
+    callback("Channel is in error state because no AMQP connection is available");
+}
+
 /**
  *  Initialize the object with an connection
  *  @param  connection