Make font hinting and antialiasing size dependent when using FontConfig

Add the pixel size of the font to the search pattern to get size dependent
font settings. This patch allows to take into account KDE settings for
font sizes which should be excluded from antialiasing.

Change-Id: I8bd8b7b3d585009d0a39db631cd02b7970537f5c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>
Fix use-after-delete bug in tst_QWidget::taskQTBUG_27643_enterEvents()

ASAN report:

  READ of size 8 at 0x606000011990 thread T0
    #0 0x505e3b in EnterTestMainDialog::eventFilter(QObject*, QEvent*) tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp:10294
    [...]

  0x606000011990 is located 48 bytes inside of 56-byte region [0x606000011960,0x606000011998)
  freed by thread T0 here:
    #0 0x2b8df3551c79 in operator delete(void*) ../../../../gcc/libsanitizer/asan/asan_new_delete.cc:92
    #1 0x418ab5 in EnterTestMainDialog::buttonPressed() tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp:10276

  previously allocated by thread T0 here:
    #0 0x2b8df3551739 in operator new(unsigned long) ../../../../gcc/libsanitizer/asan/asan_new_delete.cc:60
    #1 0x4188cf in EnterTestMainDialog::buttonPressed() tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp:10272

EnterTestMainDialog::eventFilter() checks for nullness of 'modal'
before accessing it, but buttonPressed() did not reset 'modal'
to nullptr after deletion.

Change-Id: I65562a29f8264a6996d7d615e06de1d1afb5af53
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>