Fix db_stress assertion failures on 0 byte SSTs (#4273)

Summary:
In the OnTableFileCreation() listener, assert on various TableProperties
only when file size > 0 bytes. The listener can get called even for 0
byte SSTs which have been deleted.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4273

Differential Revision: D9322738

Pulled By: anand1976

fbshipit-source-id: 17cdfb3d0da946b9a158d7328e5db1c87973956b

tools/db_stress.cc

@@ -1251,7 +1251,7 @@ class DbStressListener : public EventListener {
     assert(IsValidColumnFamilyName(info.cf_name));
     VerifyFilePath(info.file_path);
     assert(info.job_id > 0 || FLAGS_compact_files_one_in > 0);
-    if (info.status.ok()) {
+    if (info.status.ok() && info.file_size > 0) {
       assert(info.table_properties.data_size > 0);
       assert(info.table_properties.raw_key_size > 0);
       assert(info.table_properties.num_entries > 0);