Assert acount hash mmap file capacity > 0 (solana-labs#33575)

assert mmap capacity > 0

Co-authored-by: HaoranYi <haoran.yi@solana.com>

accounts-db/src/accounts_hash.rs

@@ -97,6 +97,7 @@ impl AccountHashesFile {
             // Theoretical performance optimization: write a zero to the end of
             // the file so that we won't have to resize it later, which may be
             // expensive.
+            assert!(self.capacity > 0);
             data.seek(SeekFrom::Start((self.capacity - 1) as u64))
                 .unwrap();
             data.write_all(&[0]).unwrap();