Since some functions can be optimized by reusing the buffers that they
already have instead of allocating and copying new ones, lets split
virBitmapToData to two functions where one only converts the data and
the second one is a wrapper that allocates the buffer if necessary.
A helper that never returns an error and treats bits out of bitmap range
as false.
Use it everywhere we use ignore_value on virBitmapGetBit, or loop over
the bitmap size.
This simplifies the usage in {libxl,qemu}DomainGetNumaParameters
and it's needed for consistent error reporting in virBitmapFormat.
Also remove the forgotten ATTRIBUTE_NONNULL marker.
We had an easy way to iterate set bits, but not for iterating
cleared bits.
* src/util/virbitmap.h (virBitmapNextClearBit): New prototype.
* src/util/virbitmap.c (virBitmapNextClearBit): Implement it.
* src/libvirt_private.syms (bitmap.h): Export it.
* tests/virbitmaptest.c (test4): Test it.
