`sensor list <start>` parsed start with _atoi(), whose uint32_t goes
negative as an int: a start of 4294967295 is -1 and 2147483648 is
INT_MIN. Both passed the `start >= end` guard, so the loop asked the
sensor manager for a negative index and passed the NULL it returned
to "%s=%s", undefined behaviour that picolibc happens to print as
"(null)". Rejecting a negative start closes it: ZephyrSensorManager
has one setting, so only index 0 is ever requested.
The same defect as meshcore-dev/MeshCore#3433.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
