Minus font size and m_Descent problem (for Bitmap Font Generator)

[ganaware]

I generated a bitmap font by Bitmap Font Generator, then imported it by BitmapFontImporter. But, there was someting wrong:

1. With the option "Match char height", Bitmap Font Generater wote a minus font size.
   But, BitmapFontImporter cannot handle the minus font size.
2. BitmapFontImporter didn't write the m_Descent property to a .fontsetting file.
   I think without the m_Descent, UnityEngine.UI.Text component cannnot align text to the bottom of the rect (UnityEngine.TextAnchor.Lower*).

So, I wrote a patch to fix those problems.

I tested it on Unity 5.4.4p1 for Windows 64bit.

[litefeel]

Fixed it in v1.5