src/sage/features/threejs.py: Do not fail when the version file does not exist

Author: kwankyu

src/sage/features/threejs.py

@@ -25,18 +25,22 @@ def __init__(self):
         """
         from sage.env import SAGE_SHARE, THREEJS_DIR
 
-        version = self.required_version()
-
         threejs_search_path = THREEJS_DIR or (
             os.path.join(SAGE_SHARE, "jupyter", "nbextensions", "threejs-sage"),
             os.path.join(SAGE_SHARE, "sagemath", "threejs-sage"),
             os.path.join(SAGE_SHARE, "sage", "threejs"),
             os.path.join(SAGE_SHARE, "threejs-sage")
             )
 
+        try:
+            version = self.required_version()
+            filename = os.path.join(version, "three.min.js")
+        except FileNotFoundError:
+            filename = 'unknown'
+
         StaticFile.__init__(
             self, name="threejs",
-            filename=os.path.join(version, "three.min.js"),
+            filename=filename,
             spkg="threejs",
             type="standard",
             search_path=threejs_search_path,