fix a crasher when set_kernel is used followed by add_kernel
fix a crasher when set_kernel is used followed by add_kernel

karlnapf/shogun,karlnapf/shogun,shogun-toolbox/shogun,lambday/shogun,geektoni/shogun,Saurabh7/shogun,lambday/shogun,Saurabh7/shogun,shogun-toolbox/shogun,besser82/shogun,lisitsyn/shogun,lisitsyn/shogun,lambday/shogun,geektoni/shogun,Saurabh7/shogun,geektoni/shogun,sorig/shogun,Saurabh7/shogun,besser82/shogun,lisitsyn/shogun,Saurabh7/shogun,Saurabh7/shogun,geektoni/shogun,shogun-toolbox/shogun,Saurabh7/shogun,karlnapf/shogun,besser82/shogun,sorig/shogun,Saurabh7/shogun,karlnapf/shogun,sorig/shogun,lambday/shogun,shogun-toolbox/shogun,lisitsyn/shogun,besser82/shogun,shogun-toolbox/shogun,lisitsyn/shogun,sorig/shogun,besser82/shogun,sorig/shogun,Saurabh7/shogun,besser82/shogun,shogun-toolbox/shogun,geektoni/shogun,geektoni/shogun,lisitsyn/shogun,sorig/shogun,karlnapf/shogun,karlnapf/shogun,lambday/shogun,lambday/shogun