Data URI: escape space characters as defined as excluded character in…

… RFC2396

util.go

@@ -397,16 +397,17 @@ var URLEncodingTable = [256]bool{
 }
 
 // DataURIEncodingTable is a charmap for which characters need escaping in the Data URI encoding scheme
-// Escape only non-printable characters, unicode and %, #, &. IE11 additionally requires encoding of
-// \, [, ], ", <, >, `, {, }, |, ^ which is not required by Chrome, Firefox, Opera, Edge, Safari, Yandex
+// Escape only non-printable characters, unicode and %, #, &.
+// IE11 additionally requires encoding of \, [, ], ", <, >, `, {, }, |, ^ which is not required by Chrome, Firefox, Opera, Edge, Safari, Yandex
+// To pass the HTML validator, restricted URL characters must be escaped: non-printable characters, space, <, >, #, %, "
 var DataURIEncodingTable = [256]bool{
 	// ASCII
 	true, true, true, true, true, true, true, true,
 	true, true, true, true, true, true, true, true,
 	true, true, true, true, true, true, true, true,
 	true, true, true, true, true, true, true, true,
 
-	false, false, true, true, false, true, true, false, // ", #, %, &
+	true, false, true, true, false, true, true, false, // space, ", #, %, &
 	false, false, false, false, false, false, false, false,
 	false, false, false, false, false, false, false, false,
 	false, false, false, false, true, false, true, false, // <, >