Fix a memory leak in QGLWidget::renderText

Task-number: QTBUG-32792
Change-Id: Ie9293a1919c1bdf13a5c357a8d2eac303a83d4d4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp

@@ -85,6 +85,8 @@ QGLTextureGlyphCache::~QGLTextureGlyphCache()
     qDebug(" -> ~QGLTextureGlyphCache() %p.", this);
 #endif
     delete m_blitProgram;
+    if (m_textureResource)
+        m_textureResource->free();
 }
 
 void QGLTextureGlyphCache::createTextureData(int width, int height)