When missing a core file, show a warning and treat it as an unknown crash.
When missing a core file, show a warning and treat it as an unknown crash.

Previously, it passed None as the filename to crashWatcher, resulting in a TypeError.

MozillaSecurity/funfuzz,nth10sd/funfuzz,nth10sd/funfuzz,nth10sd/funfuzz,MozillaSecurity/funfuzz,MozillaSecurity/funfuzz