Remove the error message `no text found in paragraph'. Aaron Brown

Remove the error message `no text found in paragraph'. Aaron Brown
points out that it's perfectly possible to generate an empty
paragraph using legal Halibut syntax: a paragraph containing nothing
but a \#{...} comment will do the job, and is quite likely to happen
if you've commented out a load of Halibut code. Therefore, an empty
paragraph is now silently ignored rather than being an error
condition in itself; if you create an empty paragraph due to it
containing an unrecognised directive, then you'll get an error for
_that_ and only that.

git-svn-id: svn://svn.tartarus.org/sgt/halibut@6361 cda61777-01e9-0310-a592-d414129be87e