windows: fix uninitialized memory access in uv_update_time()
windows: fix uninitialized memory access in uv_update_time()

uv_update_time does not overwrite the high 32 bits of uv_loop_t.time.
It merely increments it by one when the low 32 bits have wrapped. That
means that `time` needs to be initialized to zero before
uv_update_time() is called for the first time.

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