Preserve empty class and sourcefile nodes in XML report

[Godin]

Fixes #806

Our own XML report before this change is 915700 bytes, after is 920811 - increase is just 0.6%.

[marchof]

As we have this snippet now all over the place:

coverage.getInstructionCounter().getTotalCount() == 0

I would like to propose to add a new method to ICoverageNode:

/**
 * Checks whether this is an empty node.
 * 
 * @return <code>true</code> is this node does not contain any instructions
 */
boolean isEmpty();

[Godin]

@marchof added

[marchof]

@Godin Thx for adding isEmpty(). I found three more candidates for using it:

• org.jacoco.core.internal.analysis.ClassAnalyzer.addMethodCoverage(String, String, String, InstructionsBuilder, MethodNode)
• org.jacoco.ant.ReportTask.checkForMissingDebugInformation(ICoverageNode)
• org.jacoco.maven.ReportSupport.logBundleInfo(IBundleCoverage, Collection<IClassCoverage>)

[marchof]

Ok, I will add more isEmpty() use cases in a separate PR.

[Godin]

@marchof thanks for spotting this - made changes, hopefully correctly 😉