test: Fix AssemblyAnalyzerTest to be robust to Grok availability

[chadlwilson]

Description of Change

Currently AssemblyAnalyzerTest fails on teardown if you don't have grok available, but it does not appear to be required for the test itself.

[ERROR] org.owasp.dependencycheck.analyzer.AssemblyAnalyzerTest.testLog4Net -- Time elapsed: 0.089 s <<< ERROR!
org.owasp.dependencycheck.analyzer.exception.UnexpectedAnalysisException: java.lang.NullPointerException: Cannot invoke "java.io.File.getParentFile()" because "this.grokAssembly" is null
	at org.owasp.dependencycheck.analyzer.AssemblyAnalyzerTest.tearDown(AssemblyAnalyzerTest.java:184)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)

It's also nullable during run:

DependencyCheck/core/src/main/java/org/owasp/dependencycheck/analyzer/AssemblyAnalyzer.java

Lines 134 to 137 in 2bdd183

	if (grokAssembly == null) {
	LOGGER.warn("GrokAssembly didn't get deployed");
	return;
	}

This prevents a basic mvn package run to succeed.

Related issues

N/A

Have test cases been added to cover the new functionality?

yes