alr show --dependents does not handle abstract crates

[onox]

Running alr show --dependents gnat outputs:

Crate gnat is abstract and provided by:
   gnat_arm_elf
   gnat_avr_elf
   gnat_external
   gnat_native
   gnat_riscv64_elf

Instead I need to choose any of those names listed above to get a list of crates.