render: simplify detection of hard overrides

render: simplify detection of hard overrides

Previously each \r triggered full rescan of event string.
After this commit such scanning is done once in init_render_context().

Additionally some lines have moved around to correctly account for
state.evt_type (calculated in apply_transition_effects) and
state.explicit (used in reset_render_context).
That should fix cases with incorrectly applied style overrides
for subs with banner scrolling effect before the first \r.