quic: Fix melcstate "OVERRUN" caught by coverity

Check for MELCSTATES - 1 to get inside the branch, otherwise
(...)->rgb_state.melcstate may be up to MELCSTATES after the
pre-incrementing, which would result in an access to a position
that is out bounds of the array size MELCSTATES.
quic: Fix "UNINIT" caught by coverity

In case of the model evolution mode has a obsolete or non-valid value,
just return, avoiding then the usage of non initalized variables.
quic_family_tmpl: Fix "FORWARD_NULL" caught by coverity

Ensure the received bucket is non NULL