refactor: Fix build warnings

[jafin]

Remove the build warnings:

• (XGlyphTypface) Add in ctor that was #ifdeved for netcore-FX so it will 'use' _styleSimulations.
• (XGraphic) size can not be null remove check.
• (GlyphDataTable): Remove noop empty try block.

NOTE: These areas can be improved further, inspecting role of some of these blocks, the primary goal of this PR is to get to build with no warnings.

[codecov-commenter]

Codecov Report

Merging #259 (ffd0258) into master (14080aa) will decrease coverage by 0.01%. The diff coverage is 9.09%.

@@            Coverage Diff             @@
##           master     #259      +/-   ##
==========================================
- Coverage   26.37%   26.36%   -0.02%     
==========================================
  Files         238      238              
  Lines       23329    23331       +2     
  Branches     2808     2808              
==========================================
- Hits         6154     6151       -3     
- Misses      16684    16689       +5     
  Partials      491      491              

Impacted Files	Coverage Δ
PdfSharpCore/Drawing/XGraphics.cs	7.70% <ø> (+<0.01%)	:arrow_up:
PdfSharpCore/Fonts.OpenType/GlyphDataTable.cs	71.83% <ø> (+2.09%)	:arrow_up:
PdfSharpCore/Drawing/XGlyphTypeface.cs	55.23% <9.09%> (-5.59%)	:arrow_down:

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