Update NSPR to 4.12 and NSS to 3.23 on iOS

nss/lib/freebl/mpi/mpi.c

Index: nss/lib/freebl/mpi/mpi.c
diff --git a/nss/lib/freebl/mpi/mpi.c b/nss/lib/freebl/mpi/mpi.c
index 84f9b97b63ea408c8a85ddd52b38b88ba12863f3..ac19ead44c885e476ba1fac15c9bf56caa7aba85 100644
--- a/nss/lib/freebl/mpi/mpi.c
+++ b/nss/lib/freebl/mpi/mpi.c
@@ -1336,7 +1336,7 @@ mp_err mp_sqrt(const mp_int *a, mp_int *b)
   }
 
   /* Copy result to output parameter */
-  mp_sub_d(&x, 1, &x);
+  MP_CHECKOK(mp_sub_d(&x, 1, &x));
   s_mp_exch(&x, b);
 
  CLEANUP:
@@ -2959,8 +2959,12 @@ mp_err   s_mp_mul_2d(mp_int *mp, mp_digit d)
   dshift = d / MP_DIGIT_BIT;
   bshift = d % MP_DIGIT_BIT;
   /* bits to be shifted out of the top word */
-  mask   = ((mp_digit)~0 << (MP_DIGIT_BIT - bshift)); 
-  mask  &= MP_DIGIT(mp, MP_USED(mp) - 1);
+  if (bshift) {
+    mask = (mp_digit)~0 << (MP_DIGIT_BIT - bshift);
+    mask &= MP_DIGIT(mp, MP_USED(mp) - 1);
+  } else {
+    mask = 0;
+  }
 
   if (MP_OKAY != (res = s_mp_pad(mp, MP_USED(mp) + dshift + (mask != 0) )))
     return res;