llama.cpp picks a new random media marker per backend process. LocalAI
cached the first probe on the model config and skipped later probes when
MediaMarker was non-empty, so after SINGLE_ACTIVE eviction/reload the
prompt still used the stale marker and mtmd_tokenize failed (0 markers
vs 1 bitmap).
Re-probe whenever the model was not already resident before Load, while
still skipping the RPC on warm cache hits.
Fixes#12246
Assisted-by: Cursor:composer-2.5
Signed-off-by: leilei3167 <imleilei123@gmail.com>