Long missing LADSPA port upgrade routine

Summary (edited):

> The storage into a dedicated DOM element was introduced ten years ago with commit https://github.com/LMMS/lmms/commit/e99efd541a9dbd7b5656c769887c9d9ad94e4078 which was intended to close https://github.com/LMMS/lmms/issues/401. The commit only changed the save and load routines in src/core/LadspaControl.cpp but did not introduce any upgrades in DataFile.

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### Original post

The demo project shorties/Greshz-CoolSnip in master is different from stable-1.2 .

There is a calf flanger on the first track which doesn't seem to have upgraded correctly from an earlier version. Calf has been been bumped from Calf 0.18 -> Calf 0.90 since stable-1.2 .

The sound is glitchy and mostly seem to mute. Not unlike what you'd get with NaN related issues. It shouldn't carry on to other tracks in the mix since we remove NaN and infinite values but unfortunately it seem to not work in this case. When you bypass the flanger on track one both tracks are playing like they should apart from the missing FX.

Start by comparing the save and load handling in src/core/LadspaControl.cpp with the missing upgrade logic in DataFile, using the stable-1.2 and master versions as reference. Reproduce the issue with shorties/Greshz-CoolSnip and verify that the legacy LADSPA port data upgrades correctly without the flanger glitching or muting.

Written by the indexing model from the issue text.