add consensus merge single sample fix

Author: nhenry50

CHANGELOG.md

@@ -12,7 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [#903](https://github.com/nf-core/ampliseq/pull/903) - Corrects a broken link for _midori2-co1_ database.
 
 ### `Fixed`
-
+- [#906](https://github.com/nf-core/ampliseq/pull/906) - fix `mergepairs_strategy: "consensus"` causing an error in dada2_stats when analysing a run composed by only one sample
 - [#893](https://github.com/nf-core/ampliseq/pull/893),[#896](https://github.com/nf-core/ampliseq/pull/896),[#905](https://github.com/nf-core/ampliseq/pull/905) - Template update for nf-core/tools version 3.3.2
 - [#897](https://github.com/nf-core/ampliseq/pull/897) - Allow multiple region analysis with one sample
 - [#899](https://github.com/nf-core/ampliseq/pull/899) - With `--dada_ref_tax_custom` all chunks defined by `--dada_assign_chunksize` are now taxonomically annotated.