When running into invalid Unicode surrogate pairs the text layout code on
Windows ran into massive problems like crashes. This change detects the
situation of an invalid surrogate pair and falls back to treat it as
a simple character instead of requesting a complex glyph fallback.

(cherry picked from commit 913f1fc4)

Change-Id: I2988f4b64061d0a5df211f6f0f04b1f235fcd6a5