initialize all resp_times array entries

initialize all resp_times array entries

Before, the resp_times array was initialized starting with the
second entry, leaving the first entry uninitialized.  This is
at least confusing.  Initializing one additional int64_t value
per ping target should not add too much overhead, so do this just
to be on the safe side.

Assuming that the first array entry need not be initialized when
creating the array now, this guards against potential problems
from future code changes that do not take this unexpected special
case into account.