Fix #10394 Do not error on missing characters in "nullfont".

Add an exception to the conversion of "missing character" warnings into errors.

The PGF package deliberately uses the dummy font "nullfont" to suppress output.
Therefore, warnings about missing characters in "nullfont" are really only warnings.

Also updated the comment: "Missing character" warnigns are especially widespread
in XeTeX/LuaTeX but can also happen with "classical" 8-bit TeX.

Feel free to port this to branch.

src/LaTeX.cpp

@@ -892,9 +892,11 @@ int LaTeX::scanLogFile(TeXErrors & terr)
 						 from_local8bit("pdfTeX Error"),
 						 from_local8bit(token),
 						 child_name);
-			} else if (prefixIs(token, "Missing character: There is no ")) {
-				// XeTeX/LuaTeX error about missing glyph in selected font
-				// (bug 9610)
+			} else if (prefixIs(token, "Missing character: There is no ")
+					   && !contains(token, "nullfont")) {
+				// Warning about missing glyph in selected font
+				// may be dataloss (bug 9610)
+				// but can be ignored for 'nullfont' (bug 10394).
 				retval |= LATEX_ERROR;
 				terr.insertError(0,
 						 from_local8bit("Missing glyphs!"),

status.22x

@@ -85,6 +85,8 @@ What's new
   inoperable). (bug 10261, see http://www.lyx.org/trac/ticket/10261#comment:16
   for a workaround to KDE's bug.)
 
+- Do not issue an error on missing characters in 'nullfont' (bug 10394).
+
 
 * INTERNALS