Fix unneccessary copy and query in animatior.h

[syby119]

The auto keyword in C++ will drop the reference and top level const in the type deduction.

The following code at animator.h line 57 will cause boneInfoMap be implicitly copied from the animation's member variable.

// animator.h
// boneInfoMap will be deduced to 
// std::map<std::string,BoneInfo> boneInfoMap
auto boneInfoMap = m_CurrentAnimation->GetBoneIDMap();

// animation.h Animation::GetBoneIDMap()
inline const std::map<std::string,BoneInfo>& GetBoneIDMap()  { 
    return m_BoneInfoMap;
}

Since the CalculateBoneTransform is implemented in the recursive fashion, every access to the animation node in the node tree hierarchy will implicitly copy the boneInfoMap, which may cause performance issue.

Besides, we can save the boneInfoMap query result, instead of querying it three times

// original code
auto boneInfoMap = m_CurrentAnimation->GetBoneIDMap();
if (boneInfoMap.find(nodeName) != boneInfoMap.end())  {
    int index = boneInfoMap[nodeName].id;
    glm::mat4 offset = boneInfoMap[nodeName].offset;
    m_FinalBoneMatrices[index] = globalTransformation * offset;
}

// modified code
auto& boneInfoMap = m_CurrentAnimation->GetBoneIDMap();
auto boneInfo = boneInfoMap.find(nodeName);
if (boneInfo != boneInfoMap.end()) {
    int index = boneInfo->second.id;
    glm::mat4 offset = boneInfo->second.offset;
    m_FinalBoneMatrices[index] = globalTransformation * offset;
}