nir/lower_indirect: Bail early if modes == 0

There's no point in walking the program if we're never going to actually
lower anything.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir_lower_indirect_derefs.c

@@ -205,6 +205,9 @@ nir_lower_indirect_derefs(nir_shader *shader, nir_variable_mode modes)
 {
    bool progress = false;
 
+   if (modes == 0)
+      return false;
+
    nir_foreach_function(function, shader) {
       if (function->impl)
          progress = lower_indirects_impl(function->impl, modes) || progress;