Fix a unicode parsing error

[obelisk]

There was an error where having a query with a path like C:\users, osquery thought that was a unicode character sers after \u.

This adds a check for double backslashes and skips them if found.

What would happen before with the new testcase:

➜  osquery git:(master) ✗ ./build/darwin/osquery/osquery_tests --gtest_filter="ConversionsTests.test_unicode_unescape"
Note: Google Test filter = ConversionsTests.test_unicode_unescape
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from ConversionsTests
[ RUN      ] ConversionsTests.test_unicode_unescape
WARNING: Logging before InitGoogleLogging() is written to STDERR
W0421 11:44:52.044927 2431210368 conversions.h:212] Unescaping a string with length: 28 failed at: 3
/Users/obelisk/Documents/git_repos/osquery/osquery/core/tests/conversions_tests.cpp:74: Failure
      Expected: unescapeUnicode(test.first)
      Which is: ""
To be equal to: test.second
      Which is: "c:\\\\users\\\\obelisk\\\\file.txt"
[  FAILED  ] ConversionsTests.test_unicode_unescape (1 ms)
[----------] 1 test from ConversionsTests (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] ConversionsTests.test_unicode_unescape

 1 FAILED TEST

[facebook-github-bot]

@obelisk has updated the pull request.

[facebook-github-bot]

@obelisk has updated the pull request.

[osqueryer]

👎 The commit 48c6055 (Job results: 1348) failed one or more tests (FreeBSD).

[osqueryer]

🙅 The commit 87b3402 (Job results: 3393) failed the code audit or documentation test.

[osqueryer]

👎 The commit 87b3402 (Job results: 6906) failed one or more tests (Linux).

[osqueryer]

👎 The commit 87b3402 (Job results: 3796) failed one or more tests (Windows).

[osqueryer]

👎 The commit 87b3402 (Job results: 3797) failed one or more tests (Windows).

[osqueryer]

👎 The commit 87b3402 (Job results: 6907) failed one or more tests (Linux).

[facebook-github-bot]

@obelisk has updated the pull request. View: changes

[osqueryer]

👎 The commit cca927e (Job results: 6910) failed one or more tests (Linux).

[osqueryer]

👎 The commit cca927e (Job results: 6911) failed one or more tests (Linux).

[muffins]

nit: why the initialization?

[obelisk]

No reason

[muffins]

Mind changing it back for consistency with the code base? :)

[muffins]

LGTM, just one nit.

[facebook-github-bot]

@obelisk has updated the pull request.

[osqueryer]

👎 The commit f375deb (Job results: 6944) failed one or more tests (Linux).

[osqueryer]

👎 The commit f375deb (Job results: 6945) failed one or more tests (Linux).