fix any str ToInt64 ToUint64 panic

[fantastao]

Change-Id: Ic1690713d96940258811cdc149b1604128aa91a2

[codecov]

Codecov Report

Merging #450 into master will not change coverage by %.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #450   +/-   ##
=======================================
  Coverage   86.27%   86.27%           
=======================================
  Files          41       41           
  Lines        5106     5106           
=======================================
  Hits         4405     4405           
  Misses        565      565           
  Partials      136      136           

Impacted Files	Coverage Δ
any_str.go	96.59% <100.00%> (ø)
reflect_struct_decoder.go	80.02% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 58aeb59...bede7b9. Read the comment docs.

[fantastao]

When any.val equals "+" or "-", stringAny.ToInt64 and stringAny.ToUint64 will panic for slice bounds out of range.This commit fixed it.

[AllenX2018]

Merged. Thanks!