pldmd: Make CmdHandler have a virtual destructor

Other handlers inherit from this, so this destructor needs to be virtual
to avoid a new/delete size mismatch.

Signed-off-by: Joe Komlodi <komlodi@google.com>
Change-Id: I29f88869a17be22eeb740fe5ee192f28557fc187
diff --git a/pldmd/handler.hpp b/pldmd/handler.hpp
index 6884ee6..b2a885c 100644
--- a/pldmd/handler.hpp
+++ b/pldmd/handler.hpp
@@ -23,6 +23,8 @@
 class CmdHandler
 {
   public:
+    virtual ~CmdHandler() = default;
+
     /** @brief Invoke a PLDM command handler
      *
      *  @param[in] pldmCommand - PLDM command code