Fix field size

Fixes #32 (closed) and #31 (closed) and #3 (closed) and #7 (closed)

pystencils/cpu/cpujit.py

@@ -375,9 +375,11 @@ def create_function_boilerplate_code(parameter_info, name, ast_node, insert_chec
                 np_dtype = field.dtype.numpy_dtype
                 item_size = np_dtype.itemsize
 
-                aligned = any([a.lhs.args[2] for a in ast_node.assignments if
-                               hasattr(a, 'lhs') and isinstance(a.lhs, cast_func) and
-                               hasattr(a.lhs, 'dtype') and isinstance(a.lhs.dtype, VectorType)])
+                aligned = False
+                if ast_node.assignments:
+                    aligned = any([a.lhs.args[2] for a in ast_node.assignments
+                                   if hasattr(a, 'lhs') and isinstance(a.lhs, cast_func)
+                                   and hasattr(a.lhs, 'dtype') and isinstance(a.lhs.dtype, VectorType)])
 
                 if ast_node.instruction_set and aligned:
                     byte_width = ast_node.instruction_set['width'] * item_size