Bug 2505: assertion failed: comm.cc:350: "!fd_table[fd].closing()" (comment #12,bug...

Bug 2505: assertion failed: comm.cc:350: "!fd_table[fd].closing()" (comment #12,bug 2505)

This patch fixes the bug reported in comment #12 of bug 2505.
In the DeferredReadManager::kickARead method it is possible that the socket in
which refers a DeferredRead object has been closed, but the DeferredReadManager
is not informed yet because the related comm_close handler has not been
executed yet.
This patch checks the socket state and if it is closing just ignore the object.