Empty, optional XML elements should be handled without exception

[jenetics]

Empty XML elements of optional properties should be handled without exception. The following GPX file will trigger an NFE.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" version="1.1" creator="Jenetics TSP">
	<wpt lat="48.259124" lon="13.047988">
		<ele/>
		<name>Braunau am Inn</name>
	</wpt>
</gpx>

java.lang.NumberFormatException: empty String

	at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
	at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
	at java.lang.Double.parseDouble(Double.java:538)
	at io.jenetics.jpx.Length.parse(Length.java:201)
	at io.jenetics.jpx.WayPoint.lambda$reader$0(WayPoint.java:1302)
	at io.jenetics.jpx.XMLReaderImpl.read(XMLReader.java:356)
	at io.jenetics.jpx.XMLReaderImpl.read(XMLReader.java:336)
	at io.jenetics.jpx.GPX.read(GPX.java:734)
	at io.jenetics.jpx.GPXTest.loadEmptyGPX(GPXTest.java:71)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:86)
	at org.testng.internal.Invoker.invokeMethod(Invoker.java:643)
	at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:820)
	at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1128)
	at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:129)
	at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:112)
	at org.testng.TestRunner.privateRun(TestRunner.java:782)
	at org.testng.TestRunner.run(TestRunner.java:632)
	at org.testng.SuiteRunner.runTest(SuiteRunner.java:366)
	at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:361)
	at org.testng.SuiteRunner.privateRun(SuiteRunner.java:319)
	at org.testng.SuiteRunner.run(SuiteRunner.java:268)
	at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
	at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
	at org.testng.TestNG.runSuitesSequentially(TestNG.java:1244)
	at org.testng.TestNG.runSuitesLocally(TestNG.java:1169)
	at org.testng.TestNG.run(TestNG.java:1064)
	at org.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:72)
	at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:127)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Empty, optional elements should be ignored instead.

[jenetics]

Merged in r1.0.1 branch,