Protect min_heap_push_ against integer overflow. Converting unsigned to size_t for size of memory objects allows proper handling of very large heaps on 64 bit systems. Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org> Closes: #799 (cherry-picked) (cherry picked from commit 176fd5665512db95b1cf38fc647a7c706d80c14d)