LibHTTP: Consider a job failed if its body fails decompression

Our previous behaviour of treating the original invalid compressed body
as the decompressed response is quite silly, if the headers and response
doesn't match up, the job has failed.

Userland/Libraries/LibHTTP/Job.cpp

@@ -16,7 +16,7 @@
 
 namespace HTTP {
 
-static ByteBuffer handle_content_encoding(const ByteBuffer& buf, const String& content_encoding)
+static Optional<ByteBuffer> handle_content_encoding(const ByteBuffer& buf, const String& content_encoding)
 {
     dbgln_if(JOB_DEBUG, "Job::handle_content_encoding: buf has content_encoding={}", content_encoding);
 
@@ -29,8 +29,8 @@ static ByteBuffer handle_content_encoding(const ByteBuffer& buf, const String& c
 
         auto uncompressed = Compress::GzipDecompressor::decompress_all(buf);
         if (!uncompressed.has_value()) {
-            dbgln("Job::handle_content_encoding: Gzip::decompress() failed. Returning original buffer.");
-            return buf;
+            dbgln("Job::handle_content_encoding: Gzip::decompress() failed.");
+            return {};
         }
 
         if constexpr (JOB_DEBUG) {
@@ -54,8 +54,8 @@ static ByteBuffer handle_content_encoding(const ByteBuffer& buf, const String& c
             uncompressed = Compress::DeflateDecompressor::decompress_all(buf);
 
             if (!uncompressed.has_value()) {
-                dbgln("Job::handle_content_encoding: DeflateDecompressor::decompress_all() failed, returning original buffer.");
-                return buf;
+                dbgln("Job::handle_content_encoding: DeflateDecompressor::decompress_all() failed.");
+                return {};
             }
         }
 
@@ -389,7 +389,10 @@ void Job::finish_up()
         // FIXME: LibCompress exposes a streaming interface, so this can be resolved
         auto content_encoding = m_headers.get("Content-Encoding");
         if (content_encoding.has_value()) {
-            flattened_buffer = handle_content_encoding(flattened_buffer, content_encoding.value());
+            if (auto result = handle_content_encoding(flattened_buffer, content_encoding.value()); result.has_value())
+                flattened_buffer = result.release_value();
+            else
+                return did_fail(Core::NetworkJob::Error::TransmissionFailed);
         }
 
         m_buffered_size = flattened_buffer.size();