CFE_SB_IsValidMsgId handler default behavior fails if return not set

[skliper]

Is your feature request related to a problem? Please describe.
Any UT not setting the return for CFE_SB_IsValidMsgId will see the call fail in the unit under test:

cFE/modules/core_api/ut-stubs/src/cfe_sb_handlers.c

Lines 399 to 409 in 07fb348

	void UT_DefaultHandler_CFE_SB_IsValidMsgId(void *UserObj, UT_EntryKey_t FuncKey, const UT_StubContext_t *Context)
	{
	int32 status;
	bool return_value;
	UT_Stub_GetInt32StatusCode(Context, &status);
	return_value = status;
	UT_Stub_SetReturnValue(FuncKey, return_value);
	}

Describe the solution you'd like
<ore helpful to test against CFE_SB_INVALID_MSG_ID if the return isn't set.

Describe alternatives you've considered
None

Additional context
Just test against invalid, since max is configurable and UT's shouldn't rely on it.

Requester Info
Jacob Hageman - NASA/GSFC