erp5_corporate_identity: wait for image to be loaded

otherwise naturalWidth/naturalHeight may be 0

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/WebPage_createBookHeader.zpt

@@ -39,15 +39,13 @@ Creates the Book header.
           var y = document.getElementsByClassName(x[i]);
           for (var j=0; j<y.length; ++j) y[j].textContent = vars[x[i]];
         }
-        var z = document.getElementsByClassName("hack");
-        for (var k=0; k<z.length; ++k) {
-          var pic = z[k];
-          if (pic.naturalWidth / pic.naturalHeight <= 1) {
-            pic.style.width = "auto";
-            pic.style.maxWidth = "28mm";
-            pic.style.maxHeight = "28mm"
-            pic.style.height = "auto";
-          }
+      }
+      function setImageSize(pic) {
+        if (pic.naturalWidth / pic.naturalHeight <= 1) {
+          pic.style.width = "auto";
+          pic.style.maxWidth = "28mm";
+          pic.style.maxHeight = "28mm"
+          pic.style.height = "auto";
         }
       }
     </script>
@@ -65,7 +63,7 @@ Creates the Book header.
           <tr>
             <td>
               <div class="ci-book-header-image-wkhtmltopdf-image-wrapper">
-                <img class="hack" tal:attributes="src python: book_logo_url; alt python: book_logo_title"/>
+                <img class="hack" onload="setImageSize(event.srcElement)" tal:attributes="src python: book_logo_url; alt python: book_logo_title"/>
               </div>
             </td>
             <td>