x11/rofi-file-browser-extended: Fix build

The build fails with the following error:

FAILED: CMakeFiles/filebrowser.dir/src/filebrowser.c.o
/usr/bin/cc -D_XOPEN_SOURCE=700 -Dfilebrowser_EXPORTS -I/wrkdirs/usr/ports/x11/rofi-file-browser-extended/work/rofi-file-browser-extended-1.3.1/include -I/usr/local/include/cairo -I/usr/local/include/freetype2 -I/usr/local/include -I/usr/local/include/glib-2.0 -I/usr/local/lib/glib-2.0/include -I/usr/local/include/pixman-1 -I/usr/local/include/libpng16 -O2 -pipe -fstack-protector-strong -fno-strict-aliasing -O2 -pipe -fstack-protector-strong -fno-strict-aliasing -DNDEBUG -fPIC -MD -MT CMakeFiles/filebrowser.dir/src/filebrowser.c.o -MF CMakeFiles/filebrowser.dir/src/filebrowser.c.o.d -o CMakeFiles/filebrowser.dir/src/filebrowser.c.o -c /wrkdirs/usr/ports/x11/rofi-file-browser-extended/work/rofi-file-browser-extended-1.3.1/src/filebrowser.c
/wrkdirs/usr/ports/x11/rofi-file-browser-extended/work/rofi-file-browser-extended-1.3.1/src/filebrowser.c:380:27: error: incompatible function pointer types initializing '_mode_get_icon' (aka 'struct _cairo_surface *(*)(const struct rofi_mode *, unsigned int, unsigned int)') with an expression of type 'cairo_surface_t *(const Mode *, unsigned int, int)' (aka 'struct _cairo_surface *(const struct rofi_mode *, unsigned int, int)') [-Wincompatible-function-pointer-types]

._get_icon          = file_browser_get_icon,
                      ^~~~~~~~~~~~~~~~~~~~~

1 error generated.

So apply the patch provided at

https://github.com/marvinkreis/rofi-file-browser-extended/pull/49

and used by the Gentoo port too:

https://bugs.gentoo.org/880985

Reported by: pkg-fallout