Deleted unused assignments in Reader.

Deleted two unused assignments:

1. offset_in_block in Reader::SkipToInitialBlock().
2. in_fragmented_record in Reader::ReadRecord().

Reasons for the change:
1. offset_in_block is not read again after the if condition.
2. The kFullRecordType switch branch returns, so
   in_fragmented_record isn't read again.
3. The kFirstType switch branch sets in_fragmented_record to
   true after the if, so the write in the if is ignored.

Change contributed by @C0deAi on GitHub.

This fixes https://github.com/google/leveldb/issues/517

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=172763897

db/log_reader.cc

@@ -34,12 +34,11 @@ Reader::~Reader() {
 }
 
 bool Reader::SkipToInitialBlock() {
-  size_t offset_in_block = initial_offset_ % kBlockSize;
+  const size_t offset_in_block = initial_offset_ % kBlockSize;
   uint64_t block_start_location = initial_offset_ - offset_in_block;
 
   // Don't search a block if we'd be in the trailer
   if (offset_in_block > kBlockSize - 6) {
-    offset_in_block = 0;
     block_start_location += kBlockSize;
   }
 
@@ -99,9 +98,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
           // it could emit an empty kFirstType record at the tail end
           // of a block followed by a kFullType or kFirstType record
           // at the beginning of the next block.
-          if (scratch->empty()) {
-            in_fragmented_record = false;
-          } else {
+          if (!scratch->empty()) {
             ReportCorruption(scratch->size(), "partial record without end(1)");
           }
         }
@@ -117,9 +114,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
           // it could emit an empty kFirstType record at the tail end
           // of a block followed by a kFullType or kFirstType record
           // at the beginning of the next block.
-          if (scratch->empty()) {
-            in_fragmented_record = false;
-          } else {
+          if (!scratch->empty()) {
             ReportCorruption(scratch->size(), "partial record without end(2)");
           }
         }