Add default pref value for the Charset Detector. r=none (one-liner)

modules/libpref/src/init/all.js

@@ -252,6 +252,7 @@ pref("intl.font_encoding",                  6);     // CS_MAC_ROMAN
 
 pref("intl.charset_menu.static",           "iso-8859-1, iso-2022-jp, shift_jis, euc-jp");
 pref("intl.charset_menu.cache",            "");
+pref("intl.charset.detector",              "");
 
 pref("browser.enable_webfonts",         true);
 pref("browser.use_document_fonts",              1); // 0 = never, 1 = quick, 2 = always