journal: when dumping journal contents, react nicer to lines we can't read

If journal files are not cleanly closed it might happen that intermediaery
journal entries cannot be read. Handle this nicely, skip over the unreadable
entries, and log a debug message about it; after all we generally follow the
logic that we try to make the best of corrupted files.

src/shared/logs-show.c

@@ -287,7 +287,10 @@ static int output_short(
                 if (r < 0)
                         return r;
         }
-
+        if (r == -EBADMSG) {
+                log_debug_errno(r, "Skipping message we can't read: %m");
+                return 0;
+        }
         if (r < 0)
                 return log_error_errno(r, "Failed to get journal fields: %m");