Only read 32 bytes from /dev/urandom for a seed.

Check out the orlp/ed25519 repo's PR orlp#15 for more details: orlp#15

src/seed.c

@@ -30,6 +30,7 @@ int ed25519_create_seed(unsigned char *seed) {
         return 1;
     }
 
+    setbuf(f, NULL);
     fread(seed, 1, 32, f);
     fclose(f);
 #endif