fix bitmask overflow when using slotted components (sveltejs#4077)

Author: Conduitry

src/compiler/compile/render_dom/Renderer.ts

@@ -86,8 +86,6 @@ export default class Renderer {
 			null
 		);
 
-		this.context_overflow = this.context.length > 31;
-
 		// TODO messy
 		this.blocks.forEach(block => {
 			if (block instanceof Block) {
@@ -99,6 +97,8 @@ export default class Renderer {
 
 		this.fragment.render(this.block, null, x`#nodes` as Identifier);
 
+		this.context_overflow = this.context.length > 31;
+
 		this.context.forEach(member => {
 			const { variable } = member;
 			if (variable) {

test/runtime/samples/bitmask-overflow-3/_config.js

@@ -0,0 +1,3 @@
+export default {
+	error: `A is not defined`,
+};

test/runtime/samples/bitmask-overflow-3/main.svelte

@@ -0,0 +1,4 @@
+<script>
+	let x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18, x19, x20, x21, x22, x23, x24, x25, x26, x27, x28, x29, x30, x31;
+</script>
+<A>foo</A>