Simplify add_multilib_package method

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/gather_dnf.py

@@ -688,9 +688,8 @@ class Gather(GatherBase):
         added = set()
 
         for pkg in sorted(self.result_binary_packages):
-            try:
-                self.finished_add_multilib_packages[pkg]
-            except KeyError:
+            if pkg in self.finished_add_multilib_packages:
+                continue
 
             if pkg.arch in ("noarch", "src", "nosrc"):
                 self.finished_add_multilib_packages[pkg] = None