Fix disabled items in menus having blurry text

Qt is a strange beast. This is because the fusion style draws a copy of
the text offset by 1px in the Light color from the disabled palette. Can
also be fixed by setting the light color to the window color but that
might have other undesirable effects.

src/calibre/gui2/progress_indicator/CalibreStyle.cpp

@@ -167,6 +167,10 @@ int CalibreStyle::styleHint(StyleHint hint, const QStyleOption *option, const QW
         case SH_UnderlineShortcut:
             return 0;
 #endif
+        case SH_EtchDisabledText:
+            return 0;
+        case SH_DitherDisabledText:
+            return 0;
         default:
             break;
     }