Remote: handle early return of compressed blobs uploads

This is an implementation of this REAPI spec update:
bazelbuild/remote-apis#213

Here's a bazel-remote build that can be used to test this change:
buchgr/bazel-remote#527

Fixes bazelbuild#14654

CONTRIBUTORS

@@ -20,6 +20,7 @@ Shreya Bhattarai <shreyax@google.com>
 Kevin Bierhoff <kmb@google.com>
 Klaas Boesche <klaasb@google.com>
 Phil Bordelon <sunfall@google.com>
+Mostyn Bramley-Moore <mostyn@antipode.se>
 Jon Brandvein <brandjon@google.com>
 Volker Braun <vbraun.name@gmail.com>
 Thomas Broyer <t.broyer@ltgt.net>

src/main/java/com/google/devtools/build/lib/remote/ByteStreamUploader.java

@@ -323,7 +323,7 @@ ListenableFuture<Void> start() {
               // level/algorithm, so we cannot know the expected committed offset
               long committedSize = committedOffset.get();
               long expected = chunker.getOffset();
-              if (!chunker.hasNext() && committedSize != expected) {
+              if (!chunker.hasNext() && committedSize != expected || (chunker.isCompressed() && committedSize == -1)) {
                 String message =
                     format(
                         "write incomplete: committed_size %d for %d total",