The ebuild doesn't download the patch, it should be in the ebuild's files directory already. Small patch files (i.e. most of them) are kept in the portage tree, only very large patches (say > 20K) are downloaded during merging.
The path you give looks like a local overlay, is this an ebuild you downloaded from the bugzilla or forums? If so, you need to go back and get the patch file and put it in the files directory.
"Insanity: doing the same thing over and over again and expecting different results." (Albert Einstein)