solved issue if duplicate nt_resnum at the end of the chain

@@ -273,7 +273,8 @@ class Chain:
             if self.mapping is not None:
                 self.mapping.log(f"Shifting nt_resnum numbering because of {n_dup} duplicate residues {df.iloc[i,1]}")
 
-            if df.iloc[i,1] == df.iloc[i-1,1] and df.iloc[index_last_dup + 1, 1] - 1 > df.iloc[index_last_dup, 1]:
+            try:
+                if i > 0 and index_last_dup +1 < len(df.index) and df.iloc[i,1] == df.iloc[i-1,1] and df.iloc[index_last_dup + 1, 1] - 1 > df.iloc[index_last_dup, 1]:
                     # The redundant nts are consecutive in the chain (at the begining at least), and there is a gap at the end
 
                     if duplicates.iloc[n_dup-1, 0] - duplicates.iloc[0, 0] + 1 == n_dup:
@@ -299,6 +300,12 @@ class Chain:
                     # Solution : set nt_resnum[i] to nt_resnum[i-1] + 1, and shift the following by 1.
                     df.iloc[i, 1] = 1 + df.iloc[i-1, 1]
                     df.iloc[i+1:, 1] += 1
+            except:
+                warn(f"Error with parsing of {self.chain_label} duplicate residue numbers. Ignoring it.")
+                self.delete_me = True
+                self.error_messages = f"Error with parsing of duplicate residues numbers."
+                return None
+
 
         # Search for ligands at the end of the selection
         # Drop ligands detected as residues by DSSR, by detecting several markers