eo_debug: Fix segfault when parsing EO_LIFECYCLE_DEBUG envvar

eo_debug: Fix segfault when parsing EO_LIFECYCLE_DEBUG envvar

Summary:
The 'if' block should only be executed when the string contains the colon and
something else behind, but sscanf cannot be used in this case.
If the string contained no colon, the following line with strchr(s, ':')
returns NULL and everything explodes.

Test Plan: eo_debug -l now works for me without segfaulting.

Reviewers: bu5hm4n, zmike, devilhorns, q66

Subscribers: cedric, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D6347