rar5: don't continue if the last block produced no data (#2105)

rar5: don't continue if the last block produced no data (#2105)

There appear to be RAR5 archives out in the wild that have blocks at the
end of files that don't produce any data. The code in libarchive has an
infinite loop that won't break until it processes a block that produces
data, which will end up reading past the end of the file if the last
block in the file produces no data.