Adjointing a forward-declared __qpu__ function crashes with an assertion failure rather than emitting a diagnostic.

Reproduction

prep.cpp:

#include <cudaq.h>
__qpu__ void prep(cudaq::qubit &q) { h(q); }

main.cpp:

#include <cudaq.h>
__qpu__ void prep(cudaq::qubit &q);
__qpu__ bool kernel() {
  cudaq::qubit q;
  cudaq::adjoint(prep, q);
  return mz(q);
}
int main() {}

nvq++ -c prep.cpp -o prep.o
nvq++ -c main.cpp   # crashes

Expected: a compiler error saying the kernel body is unavailable, or a trap generated in lieu of an adjointed kernel.

Actual:

Assertion `!NodePtr->isKnownSentinel()' failed.
...
ApplySpecializationPass::createAdjointVariantOf
ApplyOpSpecialization.cpp:588