Fix bug #11780.

The preamble snippets are for LaTeX and do not need to be output
with HTML.

(cherry picked from commit f044d3a359)

src/Buffer.cpp

@@ -2208,10 +2208,6 @@ void Buffer::writeLyXHTMLSource(odocstream & os,
 		if (!styles.empty())
 			os << "\n<!-- Text Class Preamble -->\n" << styles << '\n';
 
-		styles = features.getPreambleSnippets().str;
-		if (!styles.empty())
-			os << "\n<!-- Preamble Snippets -->\n" << styles << '\n';
-
 		// we will collect CSS information in a stream, and then output it
 		// either here, as part of the header, or else in a separate file.
 		odocstringstream css;

src/LaTeXFeatures.h

@@ -95,7 +95,8 @@ public:
 	void addPreambleSnippet(docstring const & snippet, bool allowdupes = false);
 	///
 	TexString getPreambleSnippets() const;
-	///
+	/// Adds CSS information for HTML export.
+	/// Note that addPreambleSnippet is for LaTeX-type export
 	void addCSSSnippet(std::string const &);
 	///
 	docstring getCSSSnippets() const;

status.23x

@@ -91,6 +91,7 @@ What's new
 
 * LYXHTML
 
+- Don't output LaTeX preamble snippets with HTML (bug 11780).
 
 
 * ADVANCED FIND AND REPLACE