Fix Issue 202 - Catch RangeError thrown by native String.fromCodePoint (js)

When using a JS engine that provides a native String.fromCodePoint ES6 implementation (e.g. SpiderMonkey), a RangeError is thrown if the codepoint is invalid.

When adding the from-code-point.js polyfill, the js implementation was modified in order to handle invalid code point by returning the 0xFFFD placeholder glyph. So this is not a real "polyfill", but an specific implementation (adapted to the parser needs).

So, if a native String.fromCodePoint implementation is availbale, the fromCodePoint function should catch the RangeError and return the 0xFFFD placeholder glyph.