Fix for issue #883

[photocyte]

Just seemed to be a null variable that wasn't initialized. Checking for null variable with an if conditional didn't seem to work, hence the initialization. If there is an easy explanation why the null check didn't work would be curious to know :) Details below:

More detailed error:

	at net.sf.mzmine.modules.projectmethods.projectload.version_2_0.PeakListOpenHandler_2_0.endElement(PeakListOpenHandler_2_0.java:278)
	at java.xml/com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:610)
	at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1718)
	at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2883)
	at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:605)
	at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:534)
	at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:888)
	at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:824)
	at java.xml/com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
	at java.xml/com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1216)
	at java.xml/com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:635)
	at java.xml/com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl.parse(SAXParserImpl.java:324)
	at java.xml/javax.xml.parsers.SAXParser.parse(SAXParser.java:197)
	at net.sf.mzmine.modules.projectmethods.projectload.version_2_0.PeakListOpenHandler_2_0.readPeakList(PeakListOpenHandler_2_0.java:115)
	at net.sf.mzmine.modules.peaklistmethods.io.xmlimport.XMLImportTask.run(XMLImportTask.java:133)
	at net.sf.mzmine.taskcontrol.impl.WorkerThread.run(WorkerThread.java:58)
Dec 11, 2020 12:10:23 AM net.sf.mzmine.taskcontrol.impl.WorkerThread run

The part of PeakListOpenHandler_2_0.java which was calling the null pointer error (referencing initialized currentAllMS2FragmentScans):

      // convert vector of allMS2FragmentScans to array
      allMS2FragmentScanNumbers = new int[currentAllMS2FragmentScans.size()];
      for (int i = 0; i < allMS2FragmentScanNumbers.length; i++) {
        allMS2FragmentScanNumbers[i] = currentAllMS2FragmentScans.get(i);
      }

      // clear all MS2 fragment scan numbers list for next peak
      currentAllMS2FragmentScans.clear();