readParts: Return error when quorum unavailable (#20389)

readParts requires that both part.N and part.N.meta files be present.
This change addresses an issue with how an error to return to the upper
layers was picked from most drives where a UploadPart operation 
had failed.

.github/workflows/replication.yaml

@@ -70,3 +70,9 @@ jobs:
           sudo sysctl net.ipv6.conf.all.disable_ipv6=0
           sudo sysctl net.ipv6.conf.default.disable_ipv6=0
           make test-versioning
+
+      - name: Test Multipart upload with failures
+        run: |
+          sudo sysctl net.ipv6.conf.all.disable_ipv6=0
+          sudo sysctl net.ipv6.conf.default.disable_ipv6=0
+          make test-multipart