Fix graph client print bad when auth failed.

[CPWstatic]

Actually, it prints nothing. But, it is better than printing an address.

$ ./bin/nebula -u=user
Password: E0304 17:57:39.003026 30347 GraphClient.cpp:49] Failed to authenticate "user":
Connection failed

[Shylock-Hg]

Close #1326

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@ba8b3f6). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master    #1867   +/-   ##
=========================================
  Coverage          ?   86.74%           
=========================================
  Files             ?      630           
  Lines             ?    58683           
  Branches          ?        0           
=========================================
  Hits              ?    50903           
  Misses            ?     7780           
  Partials          ?        0

Impacted Files	Coverage Δ
src/client/cpp/GraphClient.cpp	68.42% <0%> (ø)

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