Call SetDirty method on the back place of full-width characters.

[otani-koji]

This Pull-Request is a modification of this issue: #250

When content is full-width character, this following width is 2.
https://github.com/gdamore/tcell/blob/master/console_win.go#L758

But, SetDirty method is called only at the beginning.
So, I have modified it to call SetDirty method at the back place of full-width characters.

[codecov]

Codecov Report

Merging #251 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #251   +/-   ##
======================================
  Coverage    19.7%   19.7%           
======================================
  Files          17      17           
  Lines        1441    1441           
======================================
  Hits          284     284           
  Misses       1140    1140           
  Partials       17      17

---

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[codecov]

Codecov Report

Merging #251 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #251   +/-   ##
======================================
  Coverage    19.7%   19.7%           
======================================
  Files          17      17           
  Lines        1441    1441           
======================================
  Hits          284     284           
  Misses       1140    1140           
  Partials       17      17

---

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 aaadc57...f83036c. Read the comment docs.

[gdamore]

Does this resolve #250 ?

If so, can you change the commit comment to:

'fixes #250 Some characters disappear on Windows'

Thanks?