fix CopyFile status checks

Summary:
copied from internal diff D6156261
Closes https://github.com/facebook/rocksdb/pull/3124

Differential Revision: D6230167

Pulled By: ajkr

fbshipit-source-id: 17926bb1152d607556364e3aacfec0ef3c115748

util/file_util.cc

@@ -25,18 +25,19 @@ Status CopyFile(Env* env, const std::string& source,
   {
     unique_ptr<SequentialFile> srcfile;
     s = env->NewSequentialFile(source, &srcfile, soptions);
+    if (!s.ok()) {
+      return s;
+    }
     unique_ptr<WritableFile> destfile;
-  if (s.ok()) {
     s = env->NewWritableFile(destination, &destfile, soptions);
-  } else {
+    if (!s.ok()) {
       return s;
     }
 
     if (size == 0) {
       // default argument means copy everything
-    if (s.ok()) {
       s = env->GetFileSize(source, &size);
-    } else {
+      if (!s.ok()) {
         return s;
       }
     }
@@ -48,15 +49,14 @@ Status CopyFile(Env* env, const std::string& source,
   Slice slice;
   while (size > 0) {
     size_t bytes_to_read = std::min(sizeof(buffer), static_cast<size_t>(size));
-    if (s.ok()) {
     s = src_reader->Read(bytes_to_read, &slice, buffer);
+    if (!s.ok()) {
+      return s;
     }
-    if (s.ok()) {
     if (slice.size() == 0) {
       return Status::Corruption("file too small");
     }
     s = dest_writer->Append(slice);
-    }
     if (!s.ok()) {
       return s;
     }