fix mips fesetenv(FE_DFL_ENV) again

commit 5fc1487832e16aa2119e735a388d5f36c8c139e2 attempted to fix it,
but neglected the fact that mips has branch delay slots.

src/fenv/mips/fenv.s

@@ -59,6 +59,7 @@ fegetenv:
 fesetenv:
 	addiu   $5, $4, 1
 	beq     $5, $0, 1f
+	 nop
 	lw      $5, 0($4)
 1:	ctc1    $5, $31
 	jr      $ra