fix(IText): copypaste linebreaks

[jzburns]

This is a fix for a copy and paste bug in the textfield object. Text that contains just newlines will though an exception when pasted. The fix tests this.styles[cursorLoc.lineIndex + i] && copiedStyle[0]) are both defined.

////////////////////// example ////////////////////// 

for() {
}

////////////////////// end example ////////////////////// 

close #6841