Further reduce lock contention in LookupVolumeIdsWithFallback

Optimized two loops that were holding RLock for extended periods:

Before:
- Held RLock during entire loop iteration
- Included string parsing and cache lookups
- Could block resetVidMap for significant time with large batches

After:
- Grab vidMap pointer with brief RLock
- Release lock immediately
- Perform all loop operations on local pointer

Impact:
- First loop: Cache check on initial volumeIds
- Second loop: Double-check after singleflight wait

Benefits:
- Minimal lock hold time (just pointer copy)
- resetVidMap no longer blocked by long loops
- Better concurrent performance with large volume ID lists
- Still thread-safe (vidMap methods have internal locks)

Verified with: go test -race ./weed/wdclient/... (passes)

0 files changed, 0 insertions, 0 deletions