Error when parsing source with abstract interface

[jhaiduce]

When I try to use fortran_autodoc on a source file that uses an abstract interface, sphinx crashes with

Extension error:
Handler <function fortran_parse at 0x112981d30> for event 'builder-inited' threw an exception (exception: crackline: groupcounter(=0) is nonpositive. Check the blocks.)
make: *** [html] Error 2

Example Fortran source file:

module test
  abstract interface
  end interface
end module test

[jhaiduce]

Just realized this is probably a duplicate of #30.