Don't clear styles when setting lexer id unless it has changed

This fixes styles being cleared when using the Split Window plugin.

src/sciwrappers.c

@@ -531,8 +531,10 @@ gint sci_get_lexer(ScintillaObject *sci)
 
 void sci_set_lexer(ScintillaObject *sci, guint lexer_id)
 {
+	if (sci_get_lexer(sci) != (gint)lexer_id)
+		SSM(sci, SCI_CLEARDOCUMENTSTYLE, 0, 0);
+
 	SSM(sci, SCI_SETLEXER, lexer_id, 0);
-	SSM(sci, SCI_CLEARDOCUMENTSTYLE, 0, 0);
 }