Empty Each Blocks should have consistent behavior.

Here the `error-each-blocks-empty` behaves as expected. It throws a ParseError.
I can't get the whitespace errors to repro in the tests. They're easily seen
here: https://svelte.technology/repl?version=1.51.0&gist=e1596f9631619a689e85c80e46506692

If you uncomment each section in sequence it demonstrates the behavior. I can't
quite figure out why my examples don't work.

test/parser/samples/error-comment-unclosed/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "comment was left open",
+	"loc": {
+		"line": 1,
+		"column": 0
+	},
+	"pos": 0
+}

test/parser/samples/error-comment-unclosed/input.html

@@ -0,0 +1 @@
+<!-- an unclosed comment

test/parser/samples/error-each-blocks-empty/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "Empty block",
+	"loc": {
+		"line": 1,
+		"column": 0
+	},
+	"pos": 0
+}

test/parser/samples/error-each-blocks-empty/input.html

@@ -0,0 +1 @@
+{{#each foos as foo}}{{/each}}

test/parser/samples/error-each-blocks-keyed-whitespace/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "Empty block",
+	"loc": {
+		"line": 1,
+		"column": 0
+	},
+	"pos": 0
+}

test/parser/samples/error-each-blocks-keyed-whitespace/input.html

@@ -0,0 +1,8 @@
+{{#each foos as foo @id}}
+{{/each}}
+
+<script>
+	export default {
+		data: () => ({ foos: [] })
+	}
+</script>

test/parser/samples/error-each-blocks-whitespace/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "Empty block",
+	"loc": {
+		"line": 1,
+		"column": 0
+	},
+	"pos": 0
+}

test/parser/samples/error-each-blocks-whitespace/input.html

@@ -0,0 +1,2 @@
+{{#each foos as foo}}
+{{/each}}