Add Memory::alloc_static_zeroed to allocate memory that's filled with zeroes.

This is generally faster than `malloc` followed by `memset` / loop-set to 0.

core/io/zip_io.cpp

@@ -161,8 +161,7 @@ int zipio_testerror(voidpf opaque, voidpf stream) {
 }
 
 voidpf zipio_alloc(voidpf opaque, uInt items, uInt size) {
-	voidpf ptr = memalloc((size_t)items * size);
-	memset(ptr, 0, items * size);
+	voidpf ptr = memalloc_zeroed((size_t)items * size);
 	return ptr;
 }