fix($sanitize): strip urls starting with 'unsafe:' as opposed to 'unsafe'

Closes #12524

Author: IgorMinar

src/ngSanitize/sanitize.js

@@ -149,7 +149,7 @@ function $SanitizeProvider() {
     return function(html) {
       var buf = [];
       htmlParser(html, htmlSanitizeWriter(buf, function(uri, isImage) {
-        return !/^unsafe/.test($$sanitizeUri(uri, isImage));
+        return !/^unsafe:/.test($$sanitizeUri(uri, isImage));
       }));
       return buf.join('');
     };