title: Replace first occurence of 0 in a 2D numpy array
body: <p>I have a 2D array:</p>
  <pre><code>[[1,2,0,0],
  [4,0,9,4],
  [0,0,1,0],
  [4,6,9,0]]
  </code></pre>
  <p>is there an efficient way (without using loops) to replace every first 0 in the array, with a 1:</p>
  <pre><code>[[1,2,1,0],
  [4,1,9,4],
  [1,0,1,0],
  [4,6,9,1]]
  </code></pre>
  <p>?</p>
  <p>Thanks a lot !</p>