Fix a couple nits reported by Coverity.

An unnecessary null pointer check and uninitialized scalar fields.
Don't expect these to be actual problems, but easy enough to fix in
order to silence Coverity.

src/logging/writers/Ascii.cc

@@ -19,7 +19,10 @@ Ascii::Ascii(WriterFrontend* frontend) : WriterBackend(frontend)
 	{
 	fd = 0;
 	ascii_done = false;
+	output_to_stdout = false;
+	include_meta = false;
 	tsv = false;
+	use_json = false;
 	formatter = 0;
 	}