DisplayCommandHandler::DisplayCommandHandler : potential crash

[iusyk]

Description

The ctor DisplayCommandHandler::DisplayCommandHandler takes the followinf input parameters
-DisplayPtr display,
-ConnectorPtr connector,
-BuffersStoragePtr buffersStorage,
-EventRingBufferPtr eventBuffer
all of the parameters are the pointers (rather shared_ptr)
The problems

1. parameters must be checked for a nullptr
2. There is the following code
   LOG(mLog, DEBUG) << "Create command handler, connector name: "
   << mConnector->getName();
   Of course in the case of null pointer - this is crash

Solution

1. check all parameters for a nullptr
2. wrap the logging in block if(mConnector){}

[iusyk]

fix #131