Update markup.lua - Caught bug at 159

[alejandro-alzate]

Fixed: /usr/local/share/lua/5.1/ldoc/markup.lua:159: attempt to index local 'line' (a nil value)
By adding a check enclosing all the lines that play with line making sure is not nil

I Don't know exactly why is being triggered but i hope it helps.

[alerque]

It looks like this case can be hit if @lookup happens to be the last line in a multiline markdown block. The original code assumed it could be processed and then there would be more to process. Thanks for the fix.

[alejandro-alzate]

no problemoo