Fixes a bug due to which, when reads with a template length (column 9 in the .bam file) of 0 were provided, in some cases the coverage calculation would fail with the error "AssertionError: fragment start greater than fragmentend for read ". Fragments are now assumed to be not "properly paired" when their insert size length is 0. This may slightly change the results of LIQUORICE in cases were reads with template lengths of 0 were provided.