Update ptemcee.py: require resume file to not be zero bytes

bilby/core/sampler/ptemcee.py

@@ -414,7 +414,11 @@ class Ptemcee(MCMCSampler):
             # This is a very ugly hack to support numpy>=1.24
             ptemcee.sampler.np.float = float
 
-        if os.path.isfile(self.resume_file) and self.resume is True:
+        if (
+            os.path.isfile(self.resume_file) and
+            os.path.getsize(self.resume_file) and
+            self.resume is True
+        ):
             import dill
 
             logger.info(f"Resume data {self.resume_file} found")