#2061 Reliably crashing Scintilla-cocoa OSX Mojave Xcode 9 & 10

[John Horigan]

Steps to reproduce:
1) Launch ScintillaTest application
2) Click in Scintilla editor window
3) Press and hold e
4) When accent menu appears, type 2 to select é
5) Type option-E, then type 'g'

Scintilla::UTF32FromUTF8() throws a runtime exception because it was given "\xc2\xb4g" as a string but cannot fit it into a single utf32 code point.

[Neil Hodgson]

Fixed with [d07ee8] which breaks up the input text string into individual characters when in Unicode mode. Performed in ScintillaCocoa by calling AddCharUTF in a loop as changing AddCharUTF would have wider consequences.

There could be issues with non-Unicode encodings but a quick test worked.