reseed during level change to prevent deduction of rng state

For platforms that read from the system's random number generator,
reseed during level change, before the map of a new level is created and
after level creation has finished.

src/do.c

@@ -1420,6 +1420,7 @@ boolean at_stairs, falling, portal;
             /* we'll reach here if running in wizard mode */
             error("Cannot continue this game.");
         }
+        reseed_random();
         minit(); /* ZEROCOMP */
         getlev(fd, hackpid, new_ledger, FALSE);
         (void) nhclose(fd);

src/hacklib.c

@@ -917,6 +917,17 @@ init_random()
     set_random(seed);
 }
 
+/* Reshuffles the random number generator. */
+void
+reseed_random()
+{
+    /* only reseed if we are certain that the seed generation is unguessable
+     * by the players. */
+#ifdef DEV_RANDOM
+    init_random();
+#endif
+}
+
 time_t
 getnow()
 {

src/mklev.c

@@ -982,6 +982,8 @@ mklev()
     struct mkroom *croom;
     int ridx;
 
+    reseed_random();
+
     init_mapseen(&u.uz);
     if (getbones())
         return;
@@ -1009,6 +1011,8 @@ mklev()
        entered; rooms[].orig_rtype always retains original rtype value */
     for (ridx = 0; ridx < SIZE(rooms); ridx++)
         rooms[ridx].orig_rtype = rooms[ridx].rtype;
+
+    reseed_random();
 }
 
 void