[BUG] Caught Assertion when CompactFiles races with DeleteFiles

When we attempt to compact sst file 'A', if 'A' was accidentally deleted, an 'Assert Failed' will be triggered.

### Expected behavior
The compact operation will be aborted.

### Actual behavior
An 'Assert Failed' was triggered:
```
[ RUN ] CompactFilesTest.CompactFilesRace
compact_files_test: util/comparator.cc:277: int rocksdb::{anonymous}::ComparatorWithU64TsImpl::CompareWithoutTimestamp(const rocksdb::Slice&, bool, const rocksdb::Slice&, bool) const [with TComparator = rocksdb::{anonymous}::BytewiseComparatorImpl]: Assertion `!a_has_ts || a.size() >= ts_sz' failed.
Received signal 6 (Aborted)
Invoking GDB for stack trace...
```
### Steps to reproduce the behavior
1. Open db with 'ComparatorWithU64TsImpl' ;
2. Create a.sst, b.sst, c.sst, d.sst ;
3. CompactFiles(c.sst, d.sst) and hang before finished, Delete a.sst and b.sst at the meantime ;
4. then CompactFiles(a.sst, b.sst) .
[Link commit](https://github.com/Ruabit18/rocksdb/commit/c8bf924ede3427367f22f999c8554dd857b02e1d)