MaxScale doesn't handle errors from microhttpd

MaxScale uses microhttpd to implement the admin interface/REST API:

https://github.com/mariadb-corporation/MaxScale/blob/maxscale-2.3.9/server/core/admin.cc#L400

microhttpd allows an application to handle errors by setting an error handler by calling the MHD_set_panic_func function:

Function: void MHD_set_panic_func (MHD_PanicCallback cb, void *cls)
Set a handler for fatal errors.

cb
function to call if MHD encounters a fatal internal error. If no handler was set explicitly, MHD will call abort.

cls
closure argument for cb; the other arguments are the name of the source file, line number and a string describing the nature of the fatal error (which can be NULL)

https://www.gnu.org/software/libmicrohttpd/manual/html_node/microhttpd_002dinit.html

MaxScale doesn't seem to currently do this, so microhttpd error messages are lost. This can make problems with the admin interface more difficult to debug.