#3485 handled search error for MedGen and providing external Link.

[Bharath-kandula]

No description provided.

[TheMadBug]

As a correction to the original task, I noticed I said the URL for external links should appear like:
https://www.ncbi.nlm.nih.gov/medgen/?term=CN072330

But no reason we have to invoke MedGen's search, our external link for MedGen should be
https://www.ncbi.nlm.nih.gov/medgen/CN072330

Appologies for that, but should be a quick fix.
It would also be nice to have a comment explaining what the INVALID_INPUT constant does.
FYI PyCharm seems to be best at picking up comments in the form of triple double quote blocks e.g.