SegmentModel.clear_strands() works for merged models

mrdna/segmentmodel.py

@@ -2830,10 +2830,20 @@ class SegmentModel(ArbdModel):
         ## clear strands
         try:
             for s in self.strands:
-                self.children.remove(s)
+                try:
+                    self.children.remove(s)
+                except:
+                    pass
+        except:
+            pass
+
+        try:
             for seg in self.segments:
-                for d in ('fwd','rev'):
-                    seg.strand_pieces[d] = []
+                try:
+                    for d in ('fwd','rev'):
+                        seg.strand_pieces[d] = []
+                except:
+                    pass
         except:
             pass
         self.strands = strands = []