Fixed #5857 (strPlusChar: Crash on invalid code 'int+;')
#5875 clang ubsan errors: lib/checkassignif.cpp:58:34: runtime error: member call on null pointer of type 'Token'
TokenList: added assertion that makes sure the Preprocessor doesn't let through extended ascii wrongly.
#5875 Fix 'lib/mathlib.cpp:559:43: runtime error: division by zero'. Several fixes to MathLib::divide(): avoid division by zero, handle various representation of 0 value, use 'nan.' instead of '-nan.0'