Merge branch 'sage_features_threejs_modularization_fix' into pyodide

Author: mkoeppe

src/sage/features/threejs.py

@@ -56,8 +56,11 @@ def required_version(self):
 
         filename = os.path.join(SAGE_EXTCODE, 'threejs', 'threejs-version.txt')
 
-        with open(filename) as f:
-            return f.read().strip()
+        try:
+            with open(filename) as f:
+                return f.read().strip()
+        except FileNotFoundError:
+            return "unknown"
 
 
 def all_features():