Fix threads=1 behaviour

bilby/core/sampler/ptemcee.py

@@ -167,13 +167,17 @@ class Ptemcee(MCMCSampler):
 
         else:
             # Initialize the PTSampler
-            self.sampler = ptemcee.Sampler(
-                dim=self.ndim, logl=do_nothing_function, logp=do_nothing_function,
-                pool=self.pool, threads=self.threads, **self.sampler_init_kwargs)
+            if self.threads == 1:
+                self.sampler = ptemcee.Sampler(
+                    dim=self.ndim, logl=self.log_likelihood, logp=self.log_prior,
+                    **self.sampler_init_kwargs)
+            else:
+                self.sampler = ptemcee.Sampler(
+                    dim=self.ndim, logl=do_nothing_function, logp=do_nothing_function,
+                    pool=self.pool, threads=self.threads, **self.sampler_init_kwargs)
 
-            # Overwrite the _likeprior to improve performance with threads > 1
-            self.sampler._likeprior = LikePriorEvaluator(
-                self.search_parameter_keys, use_ratio=self.use_ratio)
+                self.sampler._likeprior = LikePriorEvaluator(
+                    self.search_parameter_keys, use_ratio=self.use_ratio)
 
             # Set up empty lists
             self.tau_list = []