Amend [54147a71/lyxgit]

Amend [54147a71/lyxgit]

If none of the optional arguments of a macro is used, there is no
following '[' after the macro name. Unfortunately, at loading time
the macro machinery is still not initialized, so the optionals()
member of InsetMathMacro is unusable. Hence, we have to track the
creation of macros with optionals as already we do for all macros.
The collected information is only used at loading time, because
the macros are dynamic and they may loose or acquire optional args.

Fixes the particular case reported at #11552.