SANITIZE method did not properly handle the case when there was only one...

... read group (NPE)
How about this?
```
// only harmonize the quality format if we have more than one read group
if (null != targetFormat) { // 1 < readGroupCount
    final FastqQualityFormat recordFormat = readGroupToFormat.get(rec.getReadGroup());
    if (!recordFormat.equals(targetFormat)) {
        final byte quals[] = rec.getBaseQualities();
        for (int i = 0; i < quals.length; i++) {
            quals[i] -= SolexaQualityConverter.ILLUMINA_TO_PHRED_SUBTRAHEND;
        }
    }
}
```