[FIX] Validação quando o peso do produto é zero

[danimaribeiro]

No description provided.

[coveralls]

Coverage decreased (-0.1%) to 40.292% when pulling 8602ede on 11-weight-frete-average into 9510fa9 on 11.0.

[codecov-io]

Codecov Report

Merging #310 into 11.0 will decrease coverage by 0.1%.
The diff coverage is 20.83%.

@@            Coverage Diff             @@
##             11.0     #310      +/-   ##
==========================================
- Coverage   40.39%   40.29%   -0.11%     
==========================================
  Files         112      112              
  Lines        3414     3430      +16     
==========================================
+ Hits         1379     1382       +3     
- Misses       2035     2048      +13

Impacted Files	Coverage Δ
weight_purchase/models/purchase_order.py	22.58% <20.83%> (-4.09%)	⬇️

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