src: Disable use of getpass() when it is not available

For example, getpass is not available on Android platform.

Change-Id: I4c3039a3fcf188fd9343d625a551d268a4a20a93
diff --git a/tools/ndnsec/util.hpp b/tools/ndnsec/util.hpp
index 6f55478..2de9ff1 100644
--- a/tools/ndnsec/util.hpp
+++ b/tools/ndnsec/util.hpp
@@ -46,6 +46,7 @@
 bool
 getPassword(std::string& password, const std::string& prompt)
 {
+#ifndef NDN_CXX_HAVE_GETPASS
   bool isReady = false;
 
   char* pw0 = 0;
@@ -78,6 +79,9 @@
     return false;
 
   return isReady;
+#else
+  return false;
+#endif // NDN_CXX_HAVE_GETPASS
 }
 
 ndn::shared_ptr<ndn::IdentityCertificate>