Media: Always add `alt` attributes to images inserted from URLs

Previously, when inserting an image from a URL, leaving the `alt`
field blank in the media modal would result in an image being
inserted into the editor without an `alt` attribute, rather than
an empty `alt`. This happened because the `props.type` would not
get set in `wp.media.string.props()` — because `attachment` is
undefined in this case — causing the image fallbacks to get
skipped.

This fixes the issue by explicitly setting `props.type` to 'image'
in `wp.media.string.image()` before filling out the rest of the
properties.

Props ambrosey, dabnpits.
Fixes #36735.
Built from https://develop.svn.wordpress.org/trunk@38065


git-svn-id: http://core.svn.wordpress.org/trunk@38006 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-editor.js

@@ -55,7 +55,14 @@
 			fallbacks = function( props ) {
 				// Generate alt fallbacks and strip tags.
 				if ( 'image' === props.type && ! props.alt ) {
-					props.alt = props.caption || props.title || '';
+					if ( props.caption ) {
+						props.alt = props.caption;
+					} else if ( props.title !== props.url ) {
+						props.alt = props.title;
+					} else {
+						props.alt = '';
+					}
+
 					props.alt = props.alt.replace( /<\/?[^>]+>/g, '' );
 					props.alt = props.alt.replace( /[\r\n]+/g, ' ' );
 				}
@@ -233,6 +240,7 @@
 			var img = {},
 				options, classes, shortcode, html;
 
+			props.type = 'image';
 			props = wp.media.string.props( props, attachment );
 			classes = props.classes || [];
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-beta3-38064';
+$wp_version = '4.6-beta3-38065';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.