Fix panic with bad urls in sync

[ldemailly]

Fixes #93

[codecov]

Codecov Report

Merging #94 into master will increase coverage by 0.4%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master     #94     +/-   ##
========================================
+ Coverage      86%   86.4%   +0.4%     
========================================
  Files           6       6             
  Lines        1371    1371             
========================================
+ Hits         1179    1184      +5     
+ Misses        137     134      -3     
+ Partials       55      53      -2

Impacted Files	Coverage Δ
fhttp/http.go	76.7% <ø> (+0.8%)	⬆️

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