fix use-of-uninitialized-value in survive_kalman_tracker_stats

[rocketmark]

Summary

integration_variance[16] is stack-allocated without initialization in survive_kalman_tracker_stats(). variance_tracker_calc() calls scalend() which divides by meas->counts and writes meas->variance.size elements. If the tracker had zero observations (no pose or IMU data was ever integrated), counts is 0 and/or variance.size is 0 — so scalend either writes NaN/Inf or writes nothing, leaving the array uninitialized. The array is then read by SV_VERBOSE via LINMATH_VEC7_EXPAND / LINMATH_VEC6_EXPAND.

Found by MSan when running test_replays (replay data with a tracker that had no observations before survive_simple_close()).

MSan report
==5058==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 survive_kalman_tracker_stats survive_kalman_tracker.c:1490
#1 survive_kalman_tracker_free survive_kalman_tracker.c:1569
#2 survive_destroy_device survive_default_devices.c:699
#3 survive_close survive.c:1043
#4 survive_simple_close survive_api.c:339

Uninitialized value was created by an allocation of 'integration_variance'
#0 survive_kalman_tracker_stats survive_kalman_tracker.c:1488

Impact

Stats-only bug. The uninitialized values are only read for debug logging (SV_VERBOSE level 5). No effect on tracking, pose output, or calibration.

Change

One line in src/survive_kalman_tracker.c:

• FLT integration_variance[16];

• FLT integration_variance[16] = {0};

[bl4ckb0ne]

Thanks!