The g_regex_match_full() method may return FALSE without setting the
GError, so that case needs to be considered.
In addition to that, the following g_assert() was not doing what it
should have been, as it was comparing the address of the variable and
not the variable itself; rework the code to avoid that as well:
g_assert (access_tech != MM_MODEM_ACCESS_TECHNOLOGY_UNKNOWN);
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