Fix #144, don't show unrelated assertion

[ttogola]

Fixes #144 by correctly setting the state after an invalid hive execute.

Whenever a fetch is invoked, there are checks in DBAPICursor.fetchone to determine whether the current state is _STATE_NONE or _STATE_FINISHED. https://github.com/dropbox/PyHive/blob/master/pyhive/common.py#L101 https://github.com/dropbox/PyHive/blob/master/pyhive/common.py#L105

On the presto side, an invalid execute results in _STATE_FINISHED and subsequent fetches return nothing. https://github.com/dropbox/PyHive/blob/master/pyhive/presto.py#L280

To keep consistency, my proposed change on the hive side also sets the state to _STATE_FINISHED when an invalid execute is detected. @jingw if we prefer that a ProgrammingError be raised I can instead set the state to _STATE_NONE such that the ProgrammingError is triggered on subsequent fetches. We could also create a new state, something like _STATE_FAILED.

(Dropbox CLA signed)

[codecov-io]

Codecov Report

Merging #172 into master will increase coverage by 0.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
+ Coverage   95.71%   95.72%   +0.01%     
==========================================
  Files          14       14              
  Lines        1422     1426       +4     
  Branches      147      147              
==========================================
+ Hits         1361     1365       +4     
  Misses         40       40              
  Partials       21       21

Impacted Files	Coverage Δ
pyhive/hive.py	90.27% <100%> (+0.18%)	:arrow_up:

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