Discard unread data of git cat-file (#29297)

Fixes #29101
Related #29298

Discard all read data to prevent misinterpreting existing data. Some
discard calls were missing in error cases.

---------

Co-authored-by: yp05327 <576951401@qq.com>

modules/git/pipeline/lfs_nogogit.go

@@ -169,6 +169,10 @@ func FindLFSFile(repo *git.Repository, objectID git.ObjectID) ([]*LFSResult, err
 				} else {
 					break commitReadingLoop
 				}
+			default:
+				if err := git.DiscardFull(batchReader, size+1); err != nil {
+					return nil, err
+				}
 			}
 		}
 	}