Partially revert "Cleanup: use post increment/decrement"

This partially reverts commit 0b2d1badec

Post increment can deep-copy for C++ iterators, while in my own checks
GCC was able to optimize this to get the same output,
better follow C++ best practice and use pre-increment for iterators.

source/blender/compositor/intern/COM_NodeOperation.cpp

@@ -152,7 +152,7 @@ NodeOperation *NodeOperation::getInputOperation(unsigned int inputSocketIndex)
 
 void NodeOperation::getConnectedInputSockets(Inputs *sockets)
 {
-  for (Inputs::const_iterator it = m_inputs.begin(); it != m_inputs.end(); it++) {
+  for (Inputs::const_iterator it = m_inputs.begin(); it != m_inputs.end(); ++it) {
     NodeOperationInput *input = *it;
     if (input->isConnected()) {
       sockets->push_back(input);