QTextEngine: Make FontEngineCache inaccessible from outside

This is really an implementation detail
and shouldn't be accessible in any way.

Change-Id: Icd9f2ea6f9a1d5ebd613ce65eebe2823301f87ea
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/gui/text/qtextengine_p.h

@@ -543,6 +543,7 @@ public:
 
     mutable QScriptLineArray lines;
 
+private:
     struct FontEngineCache {
         FontEngineCache();
         mutable QFontEngine *prevFontEngine;
@@ -560,6 +561,7 @@ public:
     };
     mutable FontEngineCache feCache;
 
+public:
     QString text;
     mutable QFont fnt;
 #ifndef QT_NO_RAWFONT