Return rather than exit on malformed -m optarg
Return rather than exit on malformed -m optarg

Signed-off-by: Iliyan Malchev <b9962a40c76f189681da2829a74a26cab77021ea@gmail.com>

google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish,google/android-cuttlefish