linux-modules: Raise an error when a kernel module cannot be found.

Previously we'd get an unhelpful backtrace like this:

  In gnu/build/linux-modules.scm:
     184:47  4 (recursive-module-dependencies _ #:lookup-module _)
      98:14  3 (module-dependencies _)
      85:18  2 (modinfo-section-contents _)
  In ice-9/ports.scm:
     439:11  1 (call-with-input-file #f #<procedure get-bytevector-al?> ?)
  In unknown file:
	     0 (open-file #f "r" #:encoding #f #:guess-encoding #f)

  ERROR: In procedure open-file:
  Wrong type (expecting string): #f
  builder for `/gnu/store/…-linux-modules.drv' failed with exit code 1

* gnu/build/linux-modules.scm (find-module-file): When MODULE cannot be
found, raise an error instead of returning #f.  This is more useful to
the user.

0 files changed, 0 insertions, 0 deletions