open-input returns nil instead of stream pointer

[jvlmdr]

The conditional form in open-input seems incorrect:

cl-portmidi/portmidi.lisp

Lines 74 to 76 in 828f94d

	(case err
	(mem-ref stream-ptr 'midi-stream)
	(error (get-error-text errnum))))))

When there is no error, it simply returns nil because there was no matching clause.

It should probably be the same as open-output:

cl-portmidi/portmidi.lisp

Lines 89 to 91 in 828f94d

	(if err
	(error (get-error-text errnum))
	(mem-ref stream-ptr 'midi-stream)))))

[chfin]

Sorry for the late reply (I completely missed this) and thanks for the bug report. Should be fixed now.