Fix error handling issues on R-devel

[gaborcsardi]

They are caused by a behavior change in saveRDS.
It always used to create the output file, but now
it does not do that any more, if the object to write
out cannot be successfully created.
See wch/r-source@9245829

Closes #37

[codecov-io]

Codecov Report

Merging #38 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage    76.7%   76.73%   +0.02%     
==========================================
  Files          43       43              
  Lines        2778     2781       +3     
==========================================
+ Hits         2131     2134       +3     
  Misses        647      647

Impacted Files	Coverage Δ
R/result.R	96.66% <100%> (+0.37%)	⬆️

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