Notatrix throws away relations in the input without heads

[ftyers]

 # sent_id = Frog_Story:69
 # text = Wan n telpukatl kwika oksipa se chihchikichi.
 # text[orig] = wan n teelpukatl kwiika oksipa see chihchikichi~.
 # text[spa] = Y el niño lleva otra vez una chiquita.
 1	Wan	_	_	_	_	_	_	_	_
-2	n	in	DET	_	_	_	det	_	_
+2	n	in	DET	_	_	_	_	_	_
 3	telpukatl	telpukatl	NOUN	_	_	_	_	_	_
 4	kwika	_	_	_	_	_	_	_	_
 5-6	oksipa	_	_	_	_	_	_	_	_
-5	o	o	AUX	_	_	_	aux	_	_
+5	o	o	AUX	_	_	_	_	_	_
 6	ksipa	_	VERB	_	_	_	_	_	_
 7	se	_	_	_	_	_	_	_	_
 8	chihchikichi	_	_	_	_	_	_	_	_
-9	.	.	PUNCT	_	_	_	punct	_	_
+9	.	.	PUNCT	_	_	_	_	_	_
 

[jonorthwash]

Expected behaviour: keep the deprel even though a dependency arc can't be drawn.

This is probably a minor design flaw in notatrix.

[jonorthwash]

Duplicate of #335.