Fallback to another DC if given is unknown

[9seconds]

This mitigates #208

[codecov-commenter]

Codecov Report

Merging #210 (fbe4d32) into master (d0f18be) will decrease coverage by 0.13%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #210      +/-   ##
==========================================
- Coverage   83.94%   83.80%   -0.14%     
==========================================
  Files          67       67              
  Lines        1850     1859       +9     
==========================================
+ Hits         1553     1558       +5     
- Misses        210      213       +3     
- Partials       87       88       +1     

Impacted Files	Coverage Δ
mtglib/proxy.go	67.08% <33.33%> (-1.51%)	⬇️
mtglib/internal/telegram/address_pool.go	100.00% <100.00%> (ø)
mtglib/internal/telegram/telegram.go	100.00% <100.00%> (ø)

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