Fix repeated slices on AbstractThreadUnsafePartition.SliceableIterator

Patch by Tyler Hobbs; reviewed by Stefania Alborghetti for CASSANDRA-10002

CHANGES.txt

@@ -1,4 +1,5 @@
 3.0.0-beta1
+ * Fix multiple slices on RowSearchers (CASSANDRA-10002)
  * Fix bug in merging of collections (CASSANDRA-10001)
  * Optimize batchlog replay to avoid full scans (CASSANDRA-7237)
  * Repair improvements when using vnodes (CASSANDRA-5220)

src/java/org/apache/cassandra/db/partitions/AbstractThreadUnsafePartition.java

@@ -325,11 +325,17 @@ public abstract class AbstractThreadUnsafePartition implements Partition, Iterab
             // Note that because a Slice.Bound can never sort equally to a Clustering, we know none of the search will
             // be a match, so we save from testing for it.
 
-            final int start = -search(slice.start(), nextIdx, rows.size()) - 1; // First index to include
+            // since the binary search starts from nextIdx, the position returned will be an offset from nextIdx; to
+            // get an absolute position, add nextIdx back in
+            int searchResult = search(slice.start(), nextIdx, rows.size());
+            final int start = nextIdx + (-searchResult - 1); // First index to include
+
             if (start >= rows.size())
                 return Collections.emptyIterator();
 
-            final int end = -search(slice.end(), start, rows.size()) - 1; // First index to exclude
+            // similarly, add start to the returned position
+            searchResult = search(slice.end(), start, rows.size());
+            final int end = start + (-searchResult - 1); // First index to exclude
 
             // Remember the end to speed up potential further slice search
             nextIdx = end;