There is such a law.
To search Texas laws, go to
http://tlo2.tlc.state.tx.us/statutes/statutes.html. From there you can find any statute.
Here's what you are looking for, I think:
§ 30.05. CRIMINAL TRESPASS. (a) A person commits an
offense if he enters or remains on or in property, including an
aircraft or other vehicle, of another without effective consent or
he enters or remains in a building of another without effective
consent and he:
(1) had notice that the entry was forbidden; ...
(f) It is a defense to prosecution under this section that:
(1) the basis on which entry on the property or land or
in the building was forbidden is that entry with a handgun was
forbidden; and
(2) the person was carrying a concealed handgun and a
license issued under Subchapter H, Chapter 411, Government Code, to
carry a concealed handgun of the same category the person was
carrying.
- Jim