fix(xds): Don't output empty XDS content entries

When outputting US TV Parental Guidelines ContentAdvisory XDS data,
the code was always calling xdsprint() for both the age rating and
the content flags (violence, language, etc). However, if there are
no content flags (e.g., for TV-G which has no additional advisories),
the content string is empty.

This caused duplicate XDS entries in the output - one with the age
rating and one with an empty string. The fix only outputs the content
string if it is not empty.

Fixes regression test 113 output mismatch.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cfsmp3

src/lib_ccx/ccx_decoders_xds.c

@@ -472,14 +472,17 @@ void xds_do_content_advisory(struct cc_subtitle *sub, struct ccx_decoders_xds_co
 	if (!a1 && a0) // US TV parental guidelines
 	{
 		xdsprint(sub, ctx, age);
-		xdsprint(sub, ctx, content);
+		if (content[0]) // Only output content if not empty
+			xdsprint(sub, ctx, content);
 		if (changed)
 		{
 			ccx_common_logging.log_ftn("\rXDS: %s\n  ", age);
-			ccx_common_logging.log_ftn("\rXDS: %s\n  ", content);
+			if (content[0])
+				ccx_common_logging.log_ftn("\rXDS: %s\n  ", content);
 		}
 		ccx_common_logging.debug_ftn(CCX_DMT_DECODER_XDS, "\rXDS: %s\n", age);
-		ccx_common_logging.debug_ftn(CCX_DMT_DECODER_XDS, "\rXDS: %s\n", content);
+		if (content[0])
+			ccx_common_logging.debug_ftn(CCX_DMT_DECODER_XDS, "\rXDS: %s\n", content);
 	}
 	if (!a0 ||			  // MPA
 	    (a0 && a1 && !Da2 && !La3) || // Canadian English Language Rating