Fix a crash in the dagger-compiler on parameterized injected types.

Otherwise dagger-compiler crashes like this:
  java.lang.NullPointerException
    at dagger.internal.codegen.InjectProcessor.getInjectedClass(InjectProcessor.java:128)
    at dagger.internal.codegen.InjectProcessor.process(InjectProcessor.java:68)
Merge pull request #144 from square/jwilson/parameterized_injectee

Fix a crash in the dagger-compiler on parameterized injected types.