Consider Patch tags in specfile parser
    
    Patch files can be uploaded to the lookaside cache and referred
    to by Patch tags in the specfile.
    The specfile parser did not consider this case, leading to an error
    if a dist-git repo has such confiration. Fixed by parsing
    the patch tags.
    
    Resolves rhbz#2010518
    
    Signed-off-by: Otto Urpelainen <oturpe@iki.fi>