Fixed Array.prototype.sort() with --debug=YES and --debug-memory=YES.

Fixed Array.prototype.sort() with --debug=YES and --debug-memory=YES.

Previously, --debug-memory=YES activated a different allocation
mechanism that was not able to properly handle the 0 size allocation.
Specifically, njs_mp_free() failed to find a block to free when the size
of the block is 0.

The fix is to alloc at least 1 byte in the --debug-memory=YES mode.