some fixes for lbmpy vectorization

Follow-up to !212 (merged) and new feature for lbmpy!65 (merged).

pystencils/cpu/vectorization.py

@@ -209,10 +209,11 @@ def insert_vector_casts(ast_node):
             if expr.func is sp.Mul and expr.args[0] == -1:
                 # special treatment for the unary minus: make sure that the -1 has the same type as the argument
                 dtype = int
-                for arg in expr.args[1:]:
-                    if type(arg) is vector_memory_access and arg.dtype.base_type.is_float():
+                for arg in expr.atoms(vector_memory_access):
+                    if arg.dtype.base_type.is_float():
                         dtype = arg.dtype.base_type.numpy_dtype.type
-                    elif type(arg) is TypedSymbol and type(arg.dtype) is VectorType and arg.dtype.base_type.is_float():
+                for arg in expr.atoms(TypedSymbol):
+                    if type(arg.dtype) is VectorType and arg.dtype.base_type.is_float():
                         dtype = arg.dtype.base_type.numpy_dtype.type
                 if dtype is not int:
                     if dtype is np.float32: