file: Move win32 utf8->wchar open wrapper to libavutil

When libavformat was changed to use the new avpriv_open function
in 51eb213d001, this silently bypassed the existing wrapper for
win32. Move the win32 wrapper into libavutil/file.c to make sure
it gets called everywhere (not just in the libavformat case).

This makes sure that non-ascii file names gets opened properly
(where file names internally are stored as utf8, but they get
converted to wchar_t and opened with _wsopen).

Signed-off-by: Martin Storsjö <martin@martin.st>
FATE: add a TAK test
Merge commit 'dfc6b5c81491abf7effb97b23af17ccf7adcd132'

* commit 'dfc6b5c81491abf7effb97b23af17ccf7adcd132':
  file: Move win32 utf8->wchar open wrapper to libavutil

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  FATE: add a TAK test

Conflicts:
	tests/fate/lossless-audio.mak

No change as we already have a tak test with luckynight-partial.tak

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/fifo: explicitly assert that a frame should have become available after request

May help tools like coverity

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>