security+tests: Fix small bugs with uninitialized and leaked memory

Change-Id: I525ac8d284783ffff08e31dc7fe2a892bfc78307
diff --git a/src/security/command-interest-signer.cpp b/src/security/command-interest-signer.cpp
index 1dfe1ce..0d2f82f 100644
--- a/src/security/command-interest-signer.cpp
+++ b/src/security/command-interest-signer.cpp
@@ -25,6 +25,11 @@
 namespace ndn {
 namespace security {
 
+CommandInterestPreparer::CommandInterestPreparer()
+  : m_lastUsedTimestamp(0)
+{
+}
+
 Name
 CommandInterestPreparer::prepareCommandInterestName(Name name)
 {