chore: return patId instead of empty string if patId cannot be converted

src/main/java/org/miracum/streams/ume/obdstofhir/mapper/ObdsToFhirMapper.java

@@ -61,6 +61,7 @@ protected static String convertId(String id) {
       convertedId = matcher.group();
     } else {
       log.warn("Identifier to convert does not have 9 digits without leading '0': " + id);
+      return id;
     }
     return convertedId;
   }