fix incorrect prefix search behavior

avoids double incrementing of end term when reading term dict
fixes #293

index/upside_down/index_reader.go

@@ -42,7 +42,7 @@ func (i *IndexReader) FieldDictRange(fieldName string, startTerm []byte, endTerm
 }
 
 func (i *IndexReader) FieldDictPrefix(fieldName string, termPrefix []byte) (index.FieldDict, error) {
-	return i.FieldDictRange(fieldName, termPrefix, incrementBytes(termPrefix))
+	return i.FieldDictRange(fieldName, termPrefix, termPrefix)
 }
 
 func (i *IndexReader) DocIDReader(start, end string) (index.DocIDReader, error) {

test/tests/basic/searches.json

@@ -477,5 +477,24 @@
 				}
 			]
 		}
+	},
+	{
+		"comment": "reproduce bug in prefix search",
+		"search": {
+			"from": 0,
+			"size": 10,
+			"query": {
+				"field": "title",
+				"prefix": "miss"
+			}
+		},
+		"result": {
+			"total_hits": 1,
+			"hits": [
+				{
+					"id": "b"
+				}
+			]
+		}
 	}
 ]