_platform/linux.py: Ensure exception is not raised when performing sandbox availability check

buildstream/_platform/linux.py

@@ -65,7 +65,10 @@ class Linux(Platform):
     #              Private Methods                 #
     ################################################
     def _local_sandbox_available(self):
-        return os.path.exists(utils.get_host_tool('bwrap')) and os.path.exists('/dev/fuse')
+        try:
+            return os.path.exists(utils.get_host_tool('bwrap')) and os.path.exists('/dev/fuse')
+        except utils.ProgramNotFoundError:
+            return False
 
     def _check_user_ns_available(self, context):
         # Here, lets check if bwrap is able to create user namespaces,