Don't skip fields when deserializing structs at root.

[Anders429]

Fixes #18.

[codecov]

Codecov Report

Merging #24 (94ead87) into dev (5c35e2d) will increase coverage by 0.00%.
The diff coverage is 98.64%.

@@           Coverage Diff            @@
##              dev      #24    +/-   ##
========================================
  Coverage   98.18%   98.19%            
========================================
  Files          45       46     +1     
  Lines       21156    21300   +144     
========================================
+ Hits        20773    20915   +142     
- Misses        383      385     +2     

Impacted Files	Coverage Δ
src/de/struct/mod.rs	98.80% <ø> (ø)
src/de/struct/root.rs	98.61% <98.61%> (ø)
src/de/mod.rs	96.49% <100.00%> (ø)
src/de/seq/field.rs	100.00% <100.00%> (ø)
src/de/struct/value.rs	97.76% <100.00%> (ø)