Valid cursor at end-of-input results in same Tell output as error state

[BrianSipos]

I appreciate the quick changes made in #223 to provide visibility into the internal cursor.

The current API, which is accurately documented in the header below, makes it impossible to distinguish between the error state and a valid cursor positioned at the end-of-input.

QCBOR/inc/qcbor/qcbor_decode.h

Lines 1054 to 1056 in b239c65

	* would be next decoded with QCBORDecode_VGetNext(). If the cursor
	* is at the end of the input or in the error state, @c UINT32_MAX is
	* returned.

In my use of this function, I need to undo the following conversion logic and requires an additional call into UsefulInputBuf_GetBufferLength(). It seems to me that this logic is not really necessary and is not as efficient as simply not including this block (and updating the documentation appropriately). The reason is that a cursor at the end-of-input is perfectly valid situation to be in, and if a user application cares about this condition it can detect it as it needs to.

QCBOR/src/qcbor_decode.c

Lines 3167 to 3172 in b239c65

	if(uCursorOffset == UsefulInputBuf_GetBufferLength(&(pMe->InBuf))) {
	return UINT32_MAX;
	} else {
	/* Cast is safe because decoder input size is restricted. */
	return (uint32_t)uCursorOffset;
	}

[laurencelundblade]

Understand your request and kind of thought about that in the back of my mind when I made the change. Thinking about it...