LibCompress: Return Optional from decompress_all method.

Author: https://github.com/asynts
Commit: 4af8eea56f
Pull-request: https://github.com/SerenityOS/serenity/pull/3455

Libraries/LibCompress/Gzip.cpp

@@ -158,7 +158,7 @@ bool GzipDecompressor::discard_or_error(size_t count)
     return true;
 }
 
-ByteBuffer GzipDecompressor::decompress_all(ReadonlyBytes bytes)
+Optional<ByteBuffer> GzipDecompressor::decompress_all(ReadonlyBytes bytes)
 {
     InputMemoryStream memory_stream { bytes };
     GzipDecompressor gzip_stream { memory_stream };