fix: an empty static file should be kept unless its related blocks are all unwound

[alexgao001]

In the scenario where we have a static file static_file_receipts_500000_999999, block 500000 contains no transaction receipts, while block 500001 has one transaction. When we trigger an unwind to block 500000, the static file is deleted even though the range of blocks has not been fully pruned yet.

When attempting to restart or unwind further, encounter the following error:

Error: nippy jar error: failed to open file "./datadir/static_files/static_file_receipts_500000_999999.conf": No such file or directory (os error 2)

This fix allows a static file to exist even if it contains no transactions.

[joshieDo]

appreciate raising this issue!

closing in favor of #11029 , since although this would solve this immediate issue, it would skip the desired file deletion for headers, along some other issues