ENH: catch OSError in RockstarDataset._is_valid

yt/frontends/rockstar/data_structures.py

@@ -115,7 +115,10 @@ def _set_code_unit_attributes(self):
     def _is_valid(cls, filename: str, *args, **kwargs) -> bool:
         if not filename.endswith(".bin"):
             return False
-        with open(filename, mode="rb") as f:
-            header = fpu.read_cattrs(f, header_dt)
-
-        return header["magic"] == 18077126535843729616
+        try:
+            with open(filename, mode="rb") as f:
+                header = fpu.read_cattrs(f, header_dt)
+        except OSError:
+            return False
+        else:
+            return header["magic"] == 18077126535843729616