Sleigh segfaults on short inputs for JVM, NDS32 and SPARC

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Three Sleigh language definitions segfault on short byte sequences. They are
almost certainly three separate defects and can be split if that is easier to
triage — they are together here because they came out of one survey and share a
shape: a small input, no exception, the process gone.

All three reproduce on `559aacdc`, which is `master` at the time of writing, and
each is a bare `translate` call with no other state.

**1. JVM — `tableswitch`**

```python
pypcode.Context("JVM:BE:32:default").translate(
bytes.fromhex("aa873b8e6f50b409"), 0x1001,
max_instructions=99999, max_bytes=8,
flags=pypcode.TranslateFlags.BB_TERMINATING)
```

`0xaa` is `tableswitch`; `0xab` (`lookupswitch`) fails the same way. Eight bytes.

**2. NDS32**

```python
pypcode.Context("NDS32:LE:32:default").translate(
bytes.fromhex("26095d273add"), 0x1010,
max_instructions=99999, max_bytes=6,
flags=pypcode.TranslateFlags.BB_TERMINATING)
```

Six bytes.

**3. SPARC**

```python
pypcode.Context("sparc:BE:32:default").translate(
bytes.fromhex("1728394a5b6c7d8e9fb0c1d2b01e0019"), 0x14,
max_instructions=99999, max_bytes=16,
flags=pypcode.TranslateFlags.BB_TERMINATING)
```

This one needs the whole run in a single `translate` call — no individual word
in that sequence crashes on its own, which I checked.

## How much weight to put on these

Less than on the PowerPC report I opened alongside this one, and I would rather
say so than oversell. That case is an ordinary `vaddubm` that a compiler emits,
and it corrupts the heap. These three are short sequences that do not correspond
to code any toolchain produces, so they are robustness findings rather than
something a user meets on real input.

They still seem worth having. A lifter is routinely pointed at binaries whose
provenance is unknown, and there the distinction between "valid code" and
"arbitrary bytes" does not hold — the caller cannot know which it has until
after the lift, and a segfault gives no opportunity to skip the block.

I have not attempted fixes and am not proposing any. Happy to retest against a
patch.