No silent error when d_head already in the configuration (#4747)

* No silent error when d_head already in the configuration

* Update src/transformers/configuration_xlnet.py
Co-authored-by: Julien Chaumond <chaumond@gmail.com>
Co-authored-by: Julien Chaumond <chaumond@gmail.com>

src/transformers/configuration_xlnet.py

@@ -163,6 +163,10 @@ class XLNetConfig(PretrainedConfig):
         self.n_layer = n_layer
         self.n_head = n_head
         assert d_model % n_head == 0
+        if "d_head" in kwargs:
+            assert kwargs["d_head"] == d_model // n_head, (
+                f"`d_head` ({kwargs['d_head']}) should be equal to `d_model // n_head` ({d_model // n_head})"
+            )
         self.d_head = d_model // n_head
         self.ff_activation = ff_activation
         self.d_inner = d_inner