No error is generated for an incorrectly built message

[104H]

The return of a call to a builder of a message type returns an int.

If an arbitrary integer is passed instead of the return of a builder object, the message is invalid, and a call to its reader will not generate any output.

For example,

boundingBox2DLabeledWithCategory = util_fb.createBoundingBox2DLabeledWithCategory(
        builder, builder.CreateString("laterAddedBB"), labelsBb
        # builder, 1, labelsBb ## Incorrect but doesn't raise an error
     )

[104H]

This issue was not resolved. The Python interface will be improved as part of other work.