Fix dangling pointer warnings in consume() for Swift 5.2+

[tscholze]

Possible fix approved by @mredlin

 /// Consume bytes from stream, return unpacked file
    ///
    /// - parameter data: data to consume
    ///
    /// - throws: TarFile.Errors
    ///
    /// - returns: tuple with filename and data on completion of a single file
    open func consume(data: [CChar]) throws -> (filename: String, data: Data)? {
        if !self.streamingMode {
            throw Errors.programmingError
        }

        return try self.buffer.withUnsafeBufferPointer { bufferPointer in
            guard let pointer = bufferPointer.baseAddress else {
                throw Errors.programmingError
            }

            if bufferPointer.count > 512 {
                let header = try self.parse(header: pointer)

                let endOffset = 512 + (header.filesize + (512 - header.filesize % 512))
                if bufferPointer.count > endOffset {
                    let data = Data(bytes: pointer.advanced(by: 512), count: header.filesize)
                    self.buffer.removeFirst(endOffset)

                    if header.isFile {
                        return (filename: header.filepath, data:data)
                    }
                }
            }
            return nil
        }
    }

[dunkelstern]

I am not up to date on recent swift changes, taking myself out of assignees