Short-circuit givens validation when it's empty

pytensor/compile/function/pfunc.py

@@ -546,6 +546,7 @@ def construct_pfunc_ins_and_outs(
                 "variables in the inputs list."
             )
 
+    if givens:
         # Check that we are not using `givens` to replace input variables, because
         # this typically does nothing, contrary to what one may expect.
         in_var_set = set(in_variables)