PYTHON: Determine toplev only for chunks with dblocks > 0.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>

python/amunpy/src/amunpy/amun.py

@@ -140,7 +140,7 @@ class Amun:
             Add additional attributes.
         """
         if not 'toplev' in self.attributes:
-            self.attributes['toplev'] = max([self.chunks[n]['levels'].max() for n in range(self.attributes['nchunks'])])
+            self.attributes['toplev'] = max([max(chunk['levels']) if chunk['dblocks'] > 0 else 1 for chunk in self.chunks.values()])
 
         if not 'xlen' in self.attributes:
             self.attributes['xlen'] = self.attributes['xmax'] - self.attributes['xmin']