oik_trace_reset_notes() should test if bw_invoke_shortcode exists

[bobbingwide]

I can't remember the exact scenario but there were instances when bw_invoke_shortcode was not available even when oik_require_lib( "oik-sc-help" ) had not worked.

I added a function_exists() for bw_invoke_shortcode() as protection.

Question:

Is this really necessary?