Fix NPE during project group creation caused by ergonomics

[mbien]

Projects can change class type due to ergonomics. Hashcode/equals matching problems make storage in sets/maps problematic.

Unbox "FeatureNonProject" since

netbeans/ergonomics/ide.ergonomics/src/org/netbeans/modules/ide/ergonomics/fod/FeatureProjectFactory.java

Lines 383 to 393 in 235b99a

	public boolean equals(Object obj) {
	if (obj instanceof Project) {
	return ((Project)obj).getProjectDirectory().equals(getProjectDirectory());
	}
	return false;
	}
	@Override
	public int hashCode() {
	return getProjectDirectory().hashCode();
	}

isn't compatible with

netbeans/java/maven/src/org/netbeans/modules/maven/NbMavenProjectImpl.java

Lines 1336 to 1355 in 235b99a

	@Override
	public int hashCode() {
	return getPOMFile().hashCode() * 13;
	}
	@Override
	public boolean equals(Object obj) {
	if (obj instanceof Project) {
	NbMavenProjectImpl impl;
	if (obj instanceof NbMavenProjectImpl) {
	impl = ((NbMavenProjectImpl) obj);
	} else {
	impl = ((Project) obj).getLookup().lookup(NbMavenProjectImpl.class);
	}
	if (impl != null) {
	return getPOMFile().equals(impl.getPOMFile());
	}
	}
	return false;
	}

discovered while implementing #8164

fixes #6011, https://issues.apache.org/jira/browse/NETBEANS-2167 and https://bz.apache.org/netbeans/show_bug.cgi?id=235897

reproducer:

1. clean NB config, don't import on start
2. open existing maven project
3. open any project file
4. create new project group -> NPE

[mbien]

something isn't working correctly. tabs close now when a pg is created for a project loaded by ergonomics. i swear this worked when i tested it :(

edit: updated the impl to unbox the Project earlier. Might have hit a hash collision which caused the Set to delegate to equals?

[eirikbakke]

Looks good, thank you! (Would be good to do just a final manual test with the latest version of the code before merging.)

[mbien]

planning to merge this today (tomorrow is freeze)