ID3v24Tag.getFields doesn't handle multiple (null-separated) values

[IJabz]

From https://java.net/jira/browse/JAUDIOTAGGER-477

ID3v2.4 specifies that text frames may contain multiple values separated by the null byte. But the iterator returned by ID3v24Tag.getFields doesn't handle multi-values correctly: it produces a single ID3v24Frame with the values concatenated together, rather than returning multiple objects as expected.