That sounds like nonsense isn't it ?
SHA1(data) is a constant for a given "data"
MD5(data) is a (different) constant for a given "data"
SHA1(MD5(data)) is thus SHA1 of a constant which gives you exactly zilch in term of improvement of (in)security. At least it is not worse.
Trying to improve on a "broken" cryptography function by combining simply does not work, especially if the theory is not well understood.
For an example, applying two different cryptographic functions after each other on some data ( f(g(data)) ) could, in theory, give you back the original data.
It's always safer to simply use the next, theoreticians-approved, well-proven, algorithm.