Unmmap all partitions after postinstall

Previous code will only unmap if postinstall finishes
successfully, move call to Unmap() to top of cleanup function.

Test: th
Change-Id: Ibb8b5cd82dbed46da1ed32a3ec370f1acbb42890
diff --git a/payload_consumer/snapshot_extent_writer.h b/payload_consumer/snapshot_extent_writer.h
index c3c64cd..c3a948e 100644
--- a/payload_consumer/snapshot_extent_writer.h
+++ b/payload_consumer/snapshot_extent_writer.h
@@ -14,6 +14,9 @@
 // limitations under the License.
 //
 
+#ifndef UPDATE_ENGINE_SNAPSHOT_EXTENT_WRITER_H_
+#define UPDATE_ENGINE_SNAPSHOT_EXTENT_WRITER_H_
+
 #include <cstdint>
 #include <vector>
 
@@ -52,3 +55,5 @@
 };
 
 }  // namespace chromeos_update_engine
+
+#endif