Add test for integer to string conversion (SQLite only)

[mloskot]

The test should cover fix submitted in #176.

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Note, the CI builds are likely to fail, because the test requires #176 fix.
Without it, garbage is written to result buffers:

nanodbc\test\sqlite_test.cpp(180): FAILED:
  REQUIRE( results.get<nanodbc::string_type>(1) == L"-128" )
with expansion:
  "65408" == "-128"