Fix segfault in Record.get() with invalid positional argument count

[apoorvdarshan]

Summary

asyncpg.Record.get() could crash the interpreter (SEGV) — or, depending on stack contents, silently return the default instead of raising TypeError — when called with an invalid number of positional arguments, e.g. r.get() or r.get("a", 2, 3).

In record_get() (asyncpg/protocol/record/recordobj.c), the wrong-argument-count else branch sets a TypeError via PyErr_Format() but does not return. Execution falls through to:

res = record_item_by_name((ApgRecordObject *)self, key, &val);

with key left uninitialized, which is undefined behavior — a native crash on release builds. The release build also emitted warning: 'key' may be used uninitialized [-Wmaybe-uninitialized].

Fix

Return NULL immediately after setting the argument-count error:

} else {
    PyErr_Format(PyExc_TypeError,
                 "Record.get() expected 1 or 2 arguments, got %zd",
                 nargs);
    return NULL;
}

Tests / Verification

• Added TestRecord::test_record_get_invalid_args in tests/test_record.py asserting TypeError for r.get(), r.get("a", 2, 3), and r.get(default=2).
• Confirmed the new test fails on pristine master (AssertionError: TypeError not raised) and passes after the fix.
• Built the C extension locally (python setup.py build_ext --inplace) and ran the full tests/test_record.py module: 26 passed. The rebuild no longer emits the 'key' may be used uninitialized warning.
• Verified the issue's reproducer now raises the expected error:

  Record.get() expected 1 or 2 arguments, got 0
  Record.get() expected 1 or 2 arguments, got 3
  

  while valid calls (r.get("a"), r.get("a", default)) are unchanged.

Fixes #1328.

Disclosure: prepared with AI assistance; reviewed and verified locally.