toolbox/modprobe: Fix fallback path when mod_dirs is empty am: e067e96d

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/23452569



Change-Id: I8d17c5e76c770682fdd3c430c4efdfb234a2fc30
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>