Split package error not detected via QualifiedNameReference

[stephan-herrmann]

In #424 a test is being added: UnnamedModuleTest.testIgnoreUnnamedModule4(), which succeeds even without the new OPTION_IgnoreUnnamedModuleForSplitPackage, which is wrong. A package conflict should be reported instead, as can be seen by variant testIgnoreUnnamedModule3() which produces the same bytecode, but using a static import instead the QualifiedNameReference.