Function fz_realloc 

pub unsafe extern "C" fn fz_realloc(
    ctx: *mut fz_context,
    p: *mut c_void,
    size: usize,
) -> *mut c_void

Reallocates a block of memory to given size. Existing contents
up to min(old_size,new_size) are maintained. The rest of the
block is uninitialised.

fz_realloc(ctx, NULL, size) behaves like fz_malloc(ctx, size).

fz_realloc(ctx, p, 0); behaves like fz_free(ctx, p).

Throws exception in the event of failure to allocate.