Compress - fix Null Pointer Exception

[eselmeister]

java.lang.NullPointerException
	at org.eclipse.swtchart.internal.compress.Compress.getCompressedXSeries(Compress.java:92)
	at org.eclipse.swtchart.internal.series.LineSeries.drawLineAndArea(LineSeries.java:386)
	at org.eclipse.swtchart.internal.series.LineSeries.draw(LineSeries.java:360)
	at org.eclipse.swtchart.internal.series.Series.draw(Series.java:574)
	at org.eclipse.swtchart.internal.PlotArea.paintControl(PlotArea.java:189)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:234)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5855)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1529)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1555)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1538)
	at org.eclipse.swt.widgets.Control.gtk_draw(Control.java:3891)
	at org.eclipse.swt.widgets.Scrollable.gtk_draw(Scrollable.java:365)
	at org.eclipse.swt.widgets.Composite.gtk_draw(Composite.java:496)
	at org.eclipse.swt.widgets.Widget.windowProc(Widget.java:2482)
	at org.eclipse.swt.widgets.Control.windowProc(Control.java:6834)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:6163)
	at org.eclipse.swt.internal.gtk3.GTK3.gtk_main_do_event(Native Method)
	at org.eclipse.swt.widgets.Display.eventProc(Display.java:1597)
	at org.eclipse.swt.internal.gtk3.GTK3.gtk_main_iteration_do(Native Method)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4514)
	at org.eclipse.swtchart.util.ChartTestCase.showChart(ChartTestCase.java:75)
	at org.eclipse.swtchart.AxisTest.testArbitraryLogScale(AxisTest.java:284)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:61)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:93)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:40)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:529)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:756)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:452)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)