Fix sub_materialize for Padded

[dlfivefifty]

No description provided.

[codecov]

Codecov Report

Merging #83 into master will increase coverage by 0.2%.
The diff coverage is 95.23%.

@@           Coverage Diff            @@
##           master     #83     +/-   ##
========================================
+ Coverage   77.39%   77.6%   +0.2%     
========================================
  Files          14      14             
  Lines        1128    1143     +15     
========================================
+ Hits          873     887     +14     
- Misses        255     256      +1

Impacted Files	Coverage Δ
src/lazyconcat.jl	83.72% <95.23%> (+0.43%)	⬆️

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