implementation can indeed be empty when cppu::writeSharedLibComponentInfo calls
getEnvironmentFromModule(mod, curEnv, "", ""), which in the final if-branch
calls getEnvironment with implementation = "".  Happens when adding desktop/qa's
test-active.oxt.  Regression introduced with
ae3a0c8d "Add .component <implementation
constructor='...' feature."

Change-Id: Ia70958e4aa18d378ff35063bdf6187f6e073b765