Tolerate more whitespace in block elements

Previously the double newlines marking a block mode element couldn’t be
interspersed with whitespace.

core/modules/parsers/wikiparser/rules/html.js

@@ -48,7 +48,7 @@ exports.parse = function() {
 	// Advance the parser position to past the tag
 	this.parser.pos = tag.end;
 	// Check for an immediately following double linebreak
-	var hasLineBreak = !tag.isSelfClosing && !!this.parseTokenRegExp(this.parser.source,this.parser.pos,/(\r?\n(?:\r?\n|$))/g);
+	var hasLineBreak = !tag.isSelfClosing && !!this.parseTokenRegExp(this.parser.source,this.parser.pos,/([^\S\n]*\r?\n(?:[^\S\n]*\r?\n|$))/g);
 	// Set whether we're in block mode
 	tag.isBlock = this.is.block || hasLineBreak;
 	// Parse the body if we need to
@@ -359,7 +359,7 @@ exports.parseTag = function(source,pos,options) {
 	pos = token.end;
 	// Check for a required line break
 	if(options.requireLineBreak) {
-		token = this.parseTokenRegExp(source,pos,/(\r?\n(?:\r?\n|$))/g);
+		token = this.parseTokenRegExp(source,pos,/([^\S\n]*\r?\n(?:[^\S\n]*\r?\n|$))/g);
 		if(!token) {
 			return null;
 		}