Fix valgrind check by initialising DeletionState.

Summary:
The valgrind error was introduced by commit
1510339e52. Initialize DeletionState
in constructor.

Test Plan: valgrind --leak-check=yes ./deletefile_test

Reviewers: igor, kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D13983

db/db_impl.h

@@ -179,6 +179,12 @@ class DBImpl : public DB {
     // the current manifest_file_number, log_number and prev_log_number
     // that corresponds to the set of files in 'live'.
     uint64_t manifest_file_number, log_number, prev_log_number;
+
+    DeletionState() {
+      manifest_file_number = 0;
+      log_number = 0;
+      prev_log_number = 0;
+    }
   };
 
   // Delete any unneeded files and stale in-memory entries.