bug#20201: 25.0.50; server-buffer-clients is not defined in minor-mode help

[Glenn Morris]

Glenn Morris wrote:

> (describe-function 'not-defined)
>
> 24.3: -> Symbol's function definition is void: not-defined   # fine
> 24.4: -> 
>   not-defined is an alias for `not-defined',
>   which is not defined.  Please make a bug report.

This is due to symbol-function no longer returning an error.
It would be good if someone could fix this for 24.5.
Probably describe-function-1 just needs an fboundp check at some point.