Support parsing damaged mkv

[at-wat]

fix #146

master branch

BenchmarkUnmarshal-32   2984522   2009 ns/op   328 B/op   41 allocs/op

this PR 18c1df0

BenchmarkUnmarshal-32   2466994   2431 ns/op   360 B/op   43 allocs/op

c66164e

BenchmarkUnmarshal-32   2302615   2602 ns/op   504 B/op   47 allocs/op

[codecov]

Codecov Report

Merging #147 (fd5e125) into master (1d0de7b) will increase coverage by 0.25%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
+ Coverage   98.96%   99.22%   +0.25%     
==========================================
  Files          22       23       +1     
  Lines        1262     1291      +29     
==========================================
+ Hits         1249     1281      +32     
+ Misses          7        5       -2     
+ Partials        6        5       -1     

Impacted Files	Coverage Δ
block.go	100.00% <100.00%> (ø)
reader.go	100.00% <100.00%> (ø)
unlacer.go	100.00% <100.00%> (+2.32%)	⬆️
unmarshal.go	98.83% <100.00%> (+0.71%)	⬆️

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[at-wat]

Using bench data: #148

master

BenchmarkUnmarshal-32   611911   9060 ns/op   2844 B/op   171 allocs/op

this PR

BenchmarkUnmarshal-32   529870   10677 ns/op   2951 B/op   176 allocs/op