change gets to return \n, to distinguish 0-byte read from empty line

ulib.c

@@ -67,9 +67,9 @@ gets(char *buf, int max)
     cc = read(0, &c, 1);
     if(cc < 1)
       break;
+    buf[i++] = c;
     if(c == '\n' || c == '\r')
       break;
-    buf[i++] = c;
   }
   buf[i] = '\0';
   return buf;