Chromatogram CDF Reader - fix NPE

[eselmeister]

!MESSAGE Cannot invoke "org.eclipse.chemclipse.model.core.IScan.getTargets()" because the return value of "net.openchrom.csd.converter.supplier.cdf.model.VendorChromatogramCSD.getScan(int)" is null
!STACK 0
java.lang.NullPointerException: Cannot invoke "org.eclipse.chemclipse.model.core.IScan.getTargets()" because the return value of "net.openchrom.csd.converter.supplier.cdf.model.VendorChromatogramCSD.getScan(int)" is null
	at net.openchrom.csd.converter.supplier.cdf.io.support.AbstractCDFChromatogramArrayReader.readPeakTable(AbstractCDFChromatogramArrayReader.java:213)
	at net.openchrom.csd.converter.supplier.cdf.io.ChromatogramReaderCSD.readChromatogram(ChromatogramReaderCSD.java:130)
	at net.openchrom.csd.converter.supplier.cdf.io.ChromatogramReaderCSD.readFile(ChromatogramReaderCSD.java:67)
	at net.openchrom.csd.converter.supplier.cdf.io.ChromatogramReaderCSD.read(ChromatogramReaderCSD.java:49)
	at net.openchrom.csd.converter.supplier.cdf.converter.ChromatogramImportConverterCSD.convert(ChromatogramImportConverterCSD.java:40)
	at org.eclipse.chemclipse.converter.chromatogram.AbstractChromatogramConverter.getChromatogram(AbstractChromatogramConverter.java:238)
	at org.eclipse.chemclipse.converter.chromatogram.AbstractChromatogramConverter.convert(AbstractChromatogramConverter.java:134)
	at org.eclipse.chemclipse.ux.extension.xxd.ui.internal.runnables.ChromatogramImportRunnable.run(ChromatogramImportRunnable.java:93)
	at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:122)