fix: SCHWED-6108 read other as CHAINTYPE_POLY

This allows the mmCIF writer to save the entity_poly.type as "other"
rater than error on an unknown type.
We can do this because there is no "other" in _entity_poly.type.
Added a comment about the risks of chain_type for reading/writing mmCIF
files.

modules/mol/base/src/chain_type.cc

@@ -59,7 +59,9 @@ ChainType ChainTypeFromString(StringRef identifier)
   } else if (StringRef("oligosaccharide", 15) == identifier) {
     return CHAINTYPE_OLIGOSACCHARIDE;
   } else if (StringRef("other", 5) == identifier) {
-    return CHAINTYPE_UNKNOWN;
+    // According to the mmCIF dictionary, "other" only exists in
+    // _entity_poly.type. Therefore, "other" can only be a generic polymer.
+    return CHAINTYPE_POLY;
   }
 
   throw Error("Unrecognised chain type descriptor found: '" +

modules/mol/base/src/chain_type.hh

@@ -28,6 +28,11 @@
 namespace ost { namespace mol {
 
 /// \enum different kinds of chains
+///
+/// Warning: this class mixes vocabulary from _entity.type and
+// _entity_poly.type, which is more detailed. As a result it cannot be used to
+/// to read/write mmCIF entity types accurately.
+
 typedef enum {
   CHAINTYPE_POLY,           ///< polymer
   CHAINTYPE_NON_POLY,       ///< non-polymer