Method fixPointers

Fleece/Core/Encoder.cc:585–597

Convert absolute offsets to relative in _items:

    // Convert absolute offsets to relative in _items:
    void Encoder::fixPointers(valueArray *items) {
        size_t pointerOrigin = nextWritePos();
        int width = items->wide ? kWide : kNarrow;
        for (Value &v : *items) {
            if (v.isPointer()) {
                ssize_t pos = v._asPointer()->offset<true>() - _base.size;
                assert(pos < (ssize_t)pointerOrigin);
                bool isExternal = (pos < 0);
                v = Pointer(pointerOrigin - pos, width, isExternal && _markExternPtrs);
            }
            pointerOrigin += width;
        }
    }

#pragma mark - ARRAYS / DICTIONARIES: