TT#71551 don't allocate zero-length memory blocks

medredis_fetch_records() allocates memory for 0 return records, which in
the calling code is understood as "no memory has been allocated",
leading to a slow leak. Returning early is correct as the mem block
pointer is set to NULL in this case.

Change-Id: I69a2d397edd15cb9e4033531a218658c7ca93b12
(cherry picked from commit 96e59f70f5)

medredis.c

@@ -750,6 +750,9 @@ int medredis_fetch_records(med_callid_t *callid,
         (*count)++;
     }
 
+    if (!*count)
+        goto no_entries;
+
     *entries = (med_entry_t*)malloc(*count * sizeof(med_entry_t));
     if (!*entries) {
         L_ERROR("Failed to allocate memory for entries (cid '%s')\n", callid->value);
@@ -769,6 +772,7 @@ int medredis_fetch_records(med_callid_t *callid,
         L_DEBUG("Added entry with cid '%s' and method '%s'\n", d->callid, d->sip_method);
     }
 
+no_entries:
     g_list_free(records);
     g_list_free_full(keys, medredis_free_keys_list);