graphics/opencv-core: unbreak after r476652

> Applying FreeBSD patches for opencv-core-3.4.1_2

No file to patch. Skipping...
1 out of 1 hunks ignored--saving rejects to modules/stereo/src/descriptor.cpp.rej
Can't create modules/stereo/src/descriptor.cpp.rej, output is in /tmp/patchr6xYigwcnNn: No such file or directory

> FreeBSD patch patch-modules_stereo_src_descriptor.cpp failed to apply cleanly.

> Patch(es) patch-modules_core_include_opencv2_core_cvdef.h patch-modules_core_include_opencv2_core_typesc.h patch-modules_core_src_utils_filesystem.cpp patch-modules_highgui_include_opencv2_highgui_highguic.h patch-modules_highgui_src_window.cpp patch-modules_highgui_src_window__gtk.cpp applied cleanly.

• Error code 1