bpo-29874: fix INCREF for possible NULL values in select_select() (GH-758)

diff --git a/Modules/selectmodule.c b/Modules/selectmodule.c
index 6ea308a..da03366 100644
--- a/Modules/selectmodule.c
+++ b/Modules/selectmodule.c
@@ -289,9 +289,9 @@
         else
             ret = PyTuple_Pack(3, ifdlist, ofdlist, efdlist);
 
-        Py_DECREF(ifdlist);
-        Py_DECREF(ofdlist);
-        Py_DECREF(efdlist);
+        Py_XDECREF(ifdlist);
+        Py_XDECREF(ofdlist);
+        Py_XDECREF(efdlist);
     }
 
   finally:
@@ -1298,7 +1298,7 @@
 
     if (PyLong_Check(pfd)
 #if IDENT_TYPE == T_UINT
-	&& PyLong_AsUnsignedLong(pfd) <= UINT_MAX
+        && PyLong_AsUnsignedLong(pfd) <= UINT_MAX
 #endif
     ) {
         self->e.ident = IDENT_AsType(pfd);