nir/foreach_block: Return false if the callback on the last block fails

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/glsl/nir/nir.c

@@ -1660,9 +1660,7 @@ nir_foreach_block(nir_function_impl *impl, nir_foreach_block_cb cb, void *state)
          return false;
    }
 
-   cb(impl->end_block, state);
-
-   return true;
+   return cb(impl->end_block, state);
 }
 
 static bool