Fix the servers crashing when suddenly exiting voting (ie everyone leaves)

src/d_netcmd.c

@@ -3216,10 +3216,9 @@ void D_PickVote(void)
 		}
 	}
 
-	key = M_RandomKey(numvotes);
-
 	if (numvotes > 0)
 	{
+		key = M_RandomKey(numvotes);
 		WRITESINT8(p, temppicks[key]);
 		WRITESINT8(p, templevels[key]);
 	}

src/y_inter.c

@@ -2011,6 +2011,14 @@ void Y_StartVote(void)
 //
 void Y_EndVote(void)
 {
+	if (nextmap >= NEXTMAP_SPECIAL)
+	{
+		// Don't leave nextmap unset if the vote is ended through
+		// weird means! (such as a dedicated server becoming empty)
+		// If nextmap was left at NEXTMAP_VOTING, we'd crash!
+		Y_VoteStops(0, 0);
+	}
+
 	Y_UnloadVoteData();
 	voteendtic = -1;
 }