[FIX] mrp: correctly replace inputs in pdf_viewer widget

In the extended template `HiddenInputFile` there are actually two inputs
(one for image only and another one).

This widget needs to replace both of them otherwise the file selector will
be opened twice.

addons/mrp/static/src/xml/mrp.xml

@@ -16,8 +16,10 @@
         </div>
     </t>
     <t t-extend="HiddenInputFile" t-name="HiddenInputPDFFile">
-        <t t-jquery="input[type='file']:first" t-operation="replace">
-            <input type="file" class="o_input_file" name="ufile" accept="application/pdf" />
+        <!-- remove the inputs and put a new one for pdf only -->
+        <t t-jquery="input[type='file']" t-operation="replace"/>
+        <t t-jquery="form" t-operation="append">
+            <input type="file" class="o_input_file" name="ufile" accept="application/pdf"/>
         </t>
     </t>
 </templates>

addons/mrp/static/tests/mrp_tests.js

@@ -31,7 +31,7 @@ QUnit.module('mrp', {
     },
 }, function () {
     QUnit.test("pdf_viewer without data", function (assert) {
-        assert.expect(3);
+        assert.expect(4);
 
         var form = createView({
             View: FormView,
@@ -48,6 +48,8 @@ QUnit.module('mrp', {
             "there should be a visible 'Upload' button");
         assert.ok(form.$('.o_field_widget iframe.o_pdfview_iframe').hasClass('o_hidden'),
             "there should be an invisible iframe");
+        assert.strictEqual(form.$('input[type="file"]').length, 1,
+            "there should be one input");
 
         form.destroy();
     });