Improve Clear(). NFC.

Was getting segfaults near here with another patch since removed from the branch.
Moving these assignments after the memfree means they still have
useful data when debugging a crash in memfree.

src/dsc.h

@@ -533,9 +533,9 @@ public:
             elem[i].Clear();
             elem[i].~T();
         }
-        elemsAllocated = n = 0;
         if(elem) MemFree(elem);
         elem = NULL;
+        elemsAllocated = n = 0;
     }
 
 };