When you have a corrupted client/installer its frustrating I know its happened to me plenty of times!
First: Do not erase the dotc setup from your computer or at least keep a backup of it somewhere. Downloading it again is very time consuming and you might have to re-install at some point again.
I found that copying the Raxan/Games folder and having at least one back up from a “good” or successfully patched client is a good idea. When you have a “good” folder, copy it and put it somewhere safe. If the first one does get corrupt just open the second folder and push (Ctrl+A) to select all inside the folder then right click and copy, then go to the first folder and hit (Ctrl+A) and right click and paste (it may ask if you wish to overwrite the files click yes). Then start the game and let it patch.