Avoid calling strlcpy when copying string onto itself

[warmenhoven]

In runloop_check_state, it calls video_shader_get_current_shader_preset to get the shader which returns runloop_st->runtime_shader_preset_path; runloop_check_state passes that to video_shader_apply_shader which calls strlcpy(runloop_st->runtime_shader_preset_path) with that value. Mac really doesn't like strlcpy() when the src and dst overlap; and in this case since they're the same pointer, it's better to just avoid the strlcpy entirely.