weegee: config: fix unmerge behavior

weegee/config.py

@@ -57,13 +57,14 @@ class WeegeeConfig:
             path = self.merges[-1][0]
             unmerges = [self.merges[-2][1]]
         else:
+            unmerges = []
             for i, (mpath, _, _) in enumerate(self.merges):
                 if mpath == path:
                     unmerges.append(self.merges[i-1][1])
                     unmerges.extend(partial for _, _, partial in self.merges[i + 1:])
                     break
             else:
-                unmerges = [self.merges[-1][1]]
+                unmerges.append(self.merges[-1][1])
 
         item = self.item
         for config in reversed(unmerges):