DeleteFilesInRange: Clean job context if no files deleted

Summary:
We need to clean the job context if we end up not deleting any
files because no files are in the range specified.

Test Plan: DBCompactionTest.DeleteFileRange

Reviewers: sdong, anthony, yhchiang, kradhakrishnan, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D52467

db/db_compaction_test.cc

@@ -1230,6 +1230,13 @@ TEST_F(DBCompactionTest, DeleteFileRange) {
     }
   }
   ASSERT_GT(deleted_count, 0);
+  begin_string = Key(5000);
+  end_string = Key(6000);
+  Slice begin1(begin_string);
+  Slice end1(end_string);
+  // Try deleting files in range which contain no keys
+  ASSERT_OK(
+      DeleteFilesInRange(db_, db_->DefaultColumnFamily(), &begin1, &end1));
 
   ASSERT_OK(
       DeleteFilesInRange(db_, db_->DefaultColumnFamily(), nullptr, nullptr));

db/db_impl.cc

@@ -5056,6 +5056,7 @@ Status DBImpl::DeleteFilesInRange(ColumnFamilyHandle* column_family,
       }
     }
     if (edit.GetDeletedFiles().empty()) {
+      job_context.Clean();
       return Status::OK();
     }
     status = versions_->LogAndApply(cfd, *cfd->GetLatestMutableCFOptions(),