Only verify source hash if there is one

Bug: 224834577
Test: th
Change-Id: I9e07322387753e423cf229a4837927bd3cee201e
diff --git a/payload_consumer/vabc_partition_writer.cc b/payload_consumer/vabc_partition_writer.cc
index 583ba4c..54aea86 100644
--- a/payload_consumer/vabc_partition_writer.cc
+++ b/payload_consumer/vabc_partition_writer.cc
@@ -273,6 +273,9 @@
   auto source_fd = std::make_shared<EintrSafeFileDescriptor>();
   TEST_AND_RETURN_FALSE_ERRNO(
       source_fd->Open(install_part_.source_path.c_str(), O_RDONLY));
+  if (!operation.has_src_sha256_hash()) {
+    return true;
+  }
   return PartitionWriter::ValidateSourceHash(
       operation, source_fd, block_size_, error);
 }