DecayingSample::decay must always return with the time current.

src/ripple/resource/impl/DecayingSample.h

@@ -63,25 +63,24 @@ private:
     // Apply exponential decay based on the specified time.
     void decay (elapsed_type now)
     {
-        if (m_value == value_type())
+        if (now == m_when)
             return;
 
+        if (m_value != value_type())
+        {
             elapsed_type n (now - m_when);
 
-        if (n == 0)
-            return;
-
             // A span larger than four times the window decays the
             // value to an insignificant amount so just reset it.
             //
             if (n > 4 * Window)
-        {
                 m_value = value_type();
-            return;
-        }
-
+            else
+            {
                 while (n--)
                     m_value -= (m_value + Window - 1) / Window;
+            }
+        }
 
         m_when = now;
     }