CASSANDRA-21692 Accord LWT can discard condition in IF statement + Journal error handling incorrectly calculates bufferPosition

[alanwang67]

1. When we have a condition on a static row and a condition on a regular row we can discard the condition on the regular row for Accord LWTs
2. L148 and L158 in

   cassandra/src/java/org/apache/cassandra/journal/EntrySerializer.java

   Line 148 in 50a10d4

   return handleReadException(e, from.position() + headerSize, syncedOffset);

   , should be start + headerSize instead of from.position() + headerSize and start + totalSize instead of from.position() respectively since crc.update(from) in readAndUpdateHeaderCrc changes the buffer's position

reviewed by for CASSANDRA-21692

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