Fix PGET Expected Byte Check

Tar files have padding. Verify the end of the file is null and only
error if there is non-null or we haven't matched content-length from
origin.

pkg/extract/tar.go

@@ -119,6 +119,24 @@ func TarFile(r *bufio.Reader, destDir string, overwrite bool) error {
 		return fmt.Errorf("error creating links: %w", err)
 	}
 
+	// Read the rest of the bytes from the archive and verify they are all null bytes
+	// This is for validation that the byte count is correct
+	padding := make([]byte, 1024)
+	for {
+		n, err := r.Read(padding)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("error reading padding bytes: %w", err)
+		}
+		for _, b := range padding[:n] {
+			if b != 0x00 {
+				return fmt.Errorf("unexpected non-null byte in padding: %x", b)
+			}
+		}
+	}
+
 	elapsed := time.Since(startTime).Seconds()
 	logger.Debug().
 		Str("extractor", "tar").