Update iso-prototype.py

src/iso-prototype.py

@@ -724,9 +724,12 @@ def build_pycdlib(args: argparse.Namespace) -> None:
         raise PrototypeError(f"Output already exists: {output}")
 
     iso = pycdlib.PyCdlib()
+    opened = False
+
     try:
         print(f"Opening source ISO: {source}")
         iso.open(str(source))
+        opened = True
 
         include_bios, include_uefi = eltorito_platforms(source)
         print(
@@ -763,7 +766,9 @@ def build_pycdlib(args: argparse.Namespace) -> None:
         print(f"Writing output ISO: {output}")
         iso.write(str(output))
     finally:
-        iso.close()
+        if opened:
+            iso.close()
+            print(f"Opening source ISO: {source}")
 
     print(f"Created {output}")