Update mmseg/apis/test.py to fix the problem of if statement.

[lartpang]

Fixed #92

[CLAassistant]

All committers have signed the CLA.

[xvjiarui]

Hi @lartpang
Thanks for your contribution.
The code looks good to me.
Could you please sign CLA?

[lartpang]

@xvjiarui I have signed it.

[codecov]

Codecov Report

Merging #93 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master      #93   +/-   ##
=======================================
  Coverage   82.04%   82.04%           
=======================================
  Files          76       76           
  Lines        3464     3464           
  Branches      529      529           
=======================================
  Hits         2842     2842           
  Misses        519      519           
  Partials      103      103           

Flag	Coverage Δ
#unittests	82.04% <0.00%> (ø)

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Impacted Files	Coverage Δ
mmseg/apis/test.py	23.80% <0.00%> (ø)

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