Parser can't fetch the DEL field.

``` xml
<record>
<metadata>
<oai_marc>
<fixfield id="FMT">XX</fixfield>
<fixfield id="LDR">-----dz--a22-----n--4500</fixfield>
<varfield id="DEL" i1=" " i2=" ">
<subfield label="a">Y</subfield>
</varfield>
</oai_marc>
</metadata>
</record>
```
