Previously set_state() -> set_meter_point() acquired the
process-lock to change meter-position, usually causing x-runs
when setting route-state.
This also fixes an issue introduced in fd414ec158. After
populating the processor list, force setting the meter-position
looks up the output streams of the processor before the meter.
However the processors are not configured. That will only happen
later from Session::post_engine_init().
---
#3 0x00007ff07b7d4102 in __GI___assert_fail at assert.c:101
#4 0x00007ff080d3224a in ARDOUR::PluginInsert::output_streams() const at ../libs/ardour/plugin_insert.cc:289
#5 0x00007ff080de8c30 in ARDOUR::Route::set_meter_point_unlocked() at ../libs/ardour/route.cc:4106
#6 0x00007ff080de8699 in ARDOUR::Route::set_meter_point(ARDOUR::MeterPoint, bool) at ../libs/ardour/route.cc:4037
#7 0x00007ff080ddfad3 in ARDOUR::Route::set_state(XMLNode const&, int) at ../libs/ardour/route.cc:269
40e3364c66