Fix duplicate time stamp bug when loading legacy schematics.

eeschema/files-io.cpp

@@ -447,6 +447,10 @@ bool SCH_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
                             !newFileFormatDlg.IsCheckBoxChecked();
             }
 
+            // Legacy schematic can have duplicate time stamps so fix that before converting
+            // to the s-expression format.
+            schematic.ReplaceDuplicateTimeStamps();
+
             // Allow the schematic to be saved to new file format without making any edits.
             OnModify();
         }