Spurious coverity memory leak error in memoize_protover_summary()

Coverity says:

** CID 1441482:  Resource leaks  (RESOURCE_LEAK)
/src/core/or/versions.c: 402 in memoize_protover_summary()


________________________________________________________________________________________________________
*** CID 1441482:  Resource leaks  (RESOURCE_LEAK)
/src/core/or/versions.c: 402 in memoize_protover_summary()
396     {
397       if (!protover_summary_map)
398         protover_summary_map = strmap_new();
399     
400       if (strmap_size(protover_summary_map) >= MAX_PROTOVER_SUMMARY_MAP_LEN) {
401         protover_summary_cache_free_all();
   CID 1441482:  Resource leaks  (RESOURCE_LEAK)
   Overwriting "protover_summary_map" in "protover_summary_map = strmap_new()" leaks the storage that "protover_summary_map" points to.
402         protover_summary_map = strmap_new();
403       }
404     
405       const protover_summary_flags_t *cached =
406         strmap_get(protover_summary_map, protocols);     

But protover_summary_cache_free_all(); frees protover_summary_map.

cc'ing nickm, because the original fix was his.