QWindowsFontEngineDirectWrite: Fix resources leaking

fontFamily has been acquired by IDWriteFont::GetFontFamily() and thus
must be released with IDWriteFontFamily::Release().

Task-number: QTBUG-26861

Change-Id: I314153f97b8b59c9ba728220f93b493b13337039
Reviewed-by: jian liang <jianliang79@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
QFontEngine: Fix cache_cost might be not initialized

Change-Id: I4cf4de5797e6623a71593e8f382496188e3abac8
Reviewed-by: jian liang <jianliang79@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>