fix(alphatex): prevent TypeError crashes on malformed bend/whammy properties

[otherwiseguy]

Sorry for the wordy noise, I was definitely not ready to submit this. I was running through test framework seeing if AI could generate a Rust port of the alphaTex parser. I told it I wanted to record any bugs we found for upstream PRs, and it instead immediately did one on my behalf before I could read it and verify the legitimacy of the issues.

Feel free to close if this isn't useful. Sorry again for sending an un-human-verified PR.

Problem

Three malformed alphaTex inputs raise an uncaught TypeError out of readScore():

C4 {b invalid (0 4)}       TypeError: Cannot read properties of undefined (reading 'arguments')
C4 {b bend invalid (0 4)}  TypeError: Cannot read properties of undefined (reading 'nodeType')
C4 {tb invalid (0 1)}      TypeError: Cannot read properties of undefined (reading 'arguments')

Every sibling case in the same test block — {dy invalid}, {ot invalid}, {gr (invalid)}, {beam invalid} and a dozen more — reports a proper diagnostic instead, so this looks unintended rather than by design.

Cause

The bend (b/be) and whammy (tb/tbe) branches of AlphaTex1LanguageHandler scan leading type/style identifiers with an unbounded loop:

while (typeAndStyle) {
    switch (p.arguments!.arguments[tbi].nodeType) {

Argument parsing only absorbs identifiers that are known values for the property, so an unknown word such as invalid starts a new property rather than being consumed as an argument. That leaves the bend/whammy property either with no argument list at all (p.arguments undefined → first crash) or with every argument already consumed as a type/style word (tbi past the end → second crash).

Fix

Bound the loop by the actual argument count, and return early from _getBendPoints when the property has no argument list (12 lines total). Malformed input now flows through the normal diagnostic path; parsed-bend behaviour is untouched.

Before / after for the three inputs: uncaught TypeError → AT212 "Unrecogized property 'invalid'" with a source position.

Tests

The three affected cases live in errors > at219 and previously snapshotted empty diagnostic arrays, because importErrorTest records whatever readScore() produces — including a crash — so the suite stayed green. Their snapshots now contain the emitted diagnostic.

Worth noting: the recorded code is AT212 (unknown property), not the block's AT219 (invalid enum value). The invalid word never reaches the bend handler as an argument, so it cannot currently be reported as a bad enum value — if AT219 is the desired diagnostic for these inputs, that would be a follow-up in argument parsing rather than the handler. Happy to move or rename the tests if you'd prefer them outside the at219 block.

test/importer, test/model and test/audio pass (1115 tests).