Fix GetWordEnd type of functions to make sure range.max is past the last index even on buffer end

src/basic/string16.cpp

@@ -19,6 +19,7 @@ bool IsSymbol(wchar_t w) {
 }
 
 bool IsNonWord(wchar_t w) {
+    if (w == '_') return false;
     bool result = IsSymbol(w) || IsWhitespace(w);
     return result;
 }