SoundFont 2: skip "marker" presets that reference no samples

[douglas-carmichael]

Problem

Commercial SoundFonts frequently include one or two presets that carry no playable content and exist only to stamp the file with the vendor or copyright. For example, an E-mu Orbit.SF2 has presets named "E-mu Systems 2007" and "DigitalSoundFactory", each with a preset zone that points at an instrument which has no instrument zones (zero samples).

Sf2Detector created an IMultisampleSource for every preset unconditionally, so these produced empty instruments in the destination format — an empty Waldorf QPAT, an empty Renoise XRNI, etc. The user noticed empty .qpat files named after those two "presets".

Fix

After building the multi-sample for a preset, skip it if it has no non-empty groups (no samples), and log which preset was skipped. This mirrors the existing guard in EnsoniqEpsAsrDetector (if (multisampleSource.getNonEmptyGroups(...).isEmpty()) continue;), so it follows an established pattern, and it fixes the problem once at the source for every destination format rather than per-creator.

if (multisampleSource.getNonEmptyGroups (false).isEmpty ())
{
    this.notifier.log ("IDS_NOTIFY_SF2_SKIP_EMPTY_PRESET", presetName);
    continue;
}

getNonEmptyGroups(false) is used (rather than true) so a preset is skipped only when it has literally no sample zones — never merely because its zones are release-triggers.

Verification

Analyzed Orbit.SF2 before/after:

• Before: 236 presets detected (incl. the two empty marker presets).
• After: 234 detected; the log shows
  Skipping SoundFont preset 'E-mu Systems 2007' because it contains no samples. and the same for DigitalSoundFactory.
• All 234 real presets are unaffected.

A new IDS_NOTIFY_SF2_SKIP_EMPTY_PRESET string is added; CHANGELOG updated.

(Note: main HEAD currently has an unrelated XMLUtils.escapeAttribute compile error in OmnisphereCreator against the vendored uitools jar; it is independent of this change — the modified Sf2Detector compiles clean.)