added check for presence of required fields. (flatc) c++ (#4316)

* added check for presence of required fields.

* updates to resolve Travis CI build error.

* fixes for resolving appveyor build errors.

* fixes for resolving appveyor build errors.

* fixes for resolving appveyor build errors.

* updates per aardappel's comments.

* updated a variable's name.

* updates per aardappel's comments.
1 file changed