Ownable: split assertion checks in two statements

[achab]

A misleading error message can happen when calling the guard assert_only_owner.

📝 Details

The function assert_only_owner currently contains two assertion statements in the same with_attr block. The associated error message only concerns the second statement. Then, when this function is called with a caller being 0, the error message is "Ownable: caller is not the owner", which is misleading.

🔢 Code to reproduce bug

Two files to reproduce it:

• main.cairo

  %lang starknet
  
  from starkware.cairo.common.cairo_builtins import HashBuiltin
  from openzeppelin.access.ownable.library import Ownable
  
  func sum{syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr}(a : felt, b : felt) -> (sum : felt):
      Ownable.assert_only_owner()
      let (sum) = a + b
      return (sum)
  end
  

• test_main.cairo

  from starkware.cairo.common.cairo_builtins import HashBuiltin
  
  from main import sum
  
  func test_sum{
      syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr
  }():
      sum(1, 2) # this raises "Ownable: caller is not the owner" instead of a message about zero address
      return ()
  end