Check if sys.path[0] is empty

[DonJayamanne]

Fixes issue #388

[codecov-io]

Codecov Report

Merging #389 into master will decrease coverage by 0.1%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #389      +/-   ##
==========================================
- Coverage   58.35%   58.25%   -0.11%     
==========================================
  Files          23       23              
  Lines        2896     2896              
==========================================
- Hits         1690     1687       -3     
- Misses       1206     1209       +3

Impacted Files	Coverage Δ
ptvsd/ipcjson.py	65.5% <0%> (-1.5%)	⬇️

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