j2534: handle null PassThruOpen parameters

[Opriego]

Summary

• add isolated regression tests for null PassThruOpen parameters
• validate pName and pDeviceID before either pointer is used
• return the J2534-defined ERR_NULL_PARAMETER instead of crashing

Problem

PassThruOpen dereferences pDeviceID in its log statement and calls
strlen(pName) while calculating MQTT topic lengths before checking whether
either pointer is NULL. As a result, invalid required pointers can cause a
segmentation fault instead of returning ERR_NULL_PARAMETER.

Fix

Set j2534_current_api_call and perform the existing null-pointer guard before
the log statement, topic-length calculations, or any other use of the input
pointers.

Testing

The regression test compiles the real src/j2534.c with function/data sections,
links with garbage collection enabled, and stubs only dependencies reachable
from PassThruOpen.

Before the fix:

0%: Checks: 2, Failures: 0, Errors: 2
test_passthru_open_rejects_null_name: Received signal 11
test_passthru_open_rejects_null_device_id: Received signal 11

After the fix:

100%: Checks: 2, Failures: 0, Errors: 0