Conversion of the registry to sqlite format fails if one of the receipt files is not compressed in bz2 format

[macosx12345@…]

After installing MacPorts 2.0, the conversion of the registry to the new sqlite format failed. It turns out this was because the receipt file of an installed and inactive port was not compressed with bzip2: the file was portname/portversion/receipt instead of portname/portversion/receipt.bz2. After compressing the receipt file, the conversion finished successfully.

(I figured this out thanks to the trick in #30611: modifying MacPorts so that the name of each processed port is printed during the conversion.)