read double value by BigDecimal

[t-mangoe]

I fixed code. I think this fix solves the issue #206 . If you like, please merge.

[codecov-io]

Codecov Report

Merging #235 into master will increase coverage by <.01%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master     #235      +/-   ##
==========================================
+ Coverage   68.46%   68.47%   +<.01%     
==========================================
  Files         107      107              
  Lines        7335     7340       +5     
  Branches     1388     1388              
==========================================
+ Hits         5022     5026       +4     
- Misses       1867     1868       +1     
  Partials      446      446

Impacted Files	Coverage Δ
...ain/java/com/jsoniter/output/StreamImplString.java	53.91% <0%> (-0.48%)	⬇️
src/main/java/com/jsoniter/IterImpl.java	66.55% <100%> (+0.44%)	⬆️

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[plokhotnyuk]

@t-mangoe where are tests that reproduces a problem with doubles?

and, why you have mixed it with the fix for surrogate pairs?