Uninitialized RAM as a PRNG seed

When a chunk of memory is newly allocated it is filled with data from 
whatever program last used it.  Is there anything wrong with using that 
to initialize a PRNG?

(Unless your runtime lib "helpfully" clears new allocations for you, of 
course.  Then you might as well just use 0 for a PRNG seed.)

Something like the following.

/*begin C-like pseudo code*/

time_t t;
size_t s;
unsigned char *m;
sha512context hash;

t = time(NULL); /* Example only.  Use something more granular. */
while(t == time(NULL));
s = (size_t)t;
s %= 524288;
s += 524288;
m = (unsigned char *)malloc(s);

sha512_init(&hash);
sha512_update(&hash, m, s);
sha512_update(&hash, t, sizeof(time_t));
sha512_final(&hash);

free(m);

initialize_prng_with_array(hash.digest, 512 / 8);

/*end C-like pseudo code*/

The system time or some other guaranteed-unique value is necessary for 
two reasons: (1) to ensure a different PRNG seed on every run, and (2) so 
another prog can't control the PRNG seed by "initializing" memory before 
we allocate it.