Avoid null-pointer failure before EAR execution context setup

[efegokdemir]

Summary

Configured EAR modules can attempt artifact resolution before their execution context is initialized. That currently produces an opaque NullPointerException when the module accesses the artifact repository.

This adds an explicit MojoFailureException with the module identity and a regression test for the uninitialized-context path.

Fixes #514

Testing

• mvn -DskipITs -Dspotless.check.skip=true -Dspotless.apply.skip=true test — passed (49 tests).
• The focused regression failed on the unchanged implementation with the reported NullPointerException and passed with this change.
• git diff --check — passed.
• The repository's Spotless check was attempted but is blocked locally by a Palantir formatter/Java incompatibility (NoSuchFieldError in com.sun.tools.javac.tree).

Notes

This contribution was developed with AI assistance. I reviewed the complete diff and verified the failure before and after the fix. No competing open PR for #514 was found.