mi: Fix undefined memcpy in mieqGrowQueue

The first time we get here, eventQueue->events is NULL:

    #0  0x000000000040cb30 in __ubsan_handle_nonnull_arg_abort@plt ()
    #1  0x0000000000494201 in mieqGrowQueue (eventQueue=0x1001640
        <miEventQueue>, new_nevents=512) at ../mi/mieq.c:129
    #2  0x0000000000494694 in mieqInit () at ../mi/mieq.c:167
    #3  0x000000000040dcba in InitInput (argc=2, argv=0x7fffffffdd28)
        at ../hw/vfb/InitInput.c:139
    #4  0x000000000056dd42 in dix_main (argc=2, argv=0x7fffffffdd28,
        envp=0x7fffffffdd40) at ../dix/main.c:248
    #5  0x000000000041704e in main (argc=2, argv=0x7fffffffdd28,
        envp=0x7fffffffdd40) at ../dix/stubmain.c:34