eliminate bad_function_call exception

Destination.cpp

@@ -527,7 +527,8 @@ namespace client
 		if (floodfill)
 		{
 			auto request = std::make_shared<LeaseSetRequest> (m_Service);
-			request->requestComplete.push_back (requestComplete);
+			if (requestComplete)
+				request->requestComplete.push_back (requestComplete);
 			auto ts = i2p::util::GetSecondsSinceEpoch ();
 			auto ret = m_LeaseSetRequests.insert (std::pair<i2p::data::IdentHash, std::shared_ptr<LeaseSetRequest> >(dest,request));
 			if (ret.second) // inserted
@@ -537,7 +538,7 @@ namespace client
 				{
 					// request failed
 					m_LeaseSetRequests.erase (ret.first);
-					requestComplete (nullptr);
+					if (requestComplete) requestComplete (nullptr);
 				}
 			}	
 			else // duplicate
@@ -547,13 +548,13 @@ namespace client
 				//ret.first->second->requestComplete.push_back (requestComplete);
 				if (ts > ret.first->second->requestTime + MAX_LEASESET_REQUEST_TIMEOUT)
 					m_LeaseSetRequests.erase (ret.first);
-				requestComplete (nullptr);
+				if (requestComplete) requestComplete (nullptr);
 			}	
 		}	
 		else
 		{	
 			LogPrint (eLogError, "Destination: Can't request LeaseSet, no floodfills found");
-			requestComplete (nullptr);
+			if (requestComplete) requestComplete (nullptr);
 		}	
 	}