in each-else, use mount/intro according to that branch's contents (#1586)

Fixes # 1559

src/compile/nodes/EachBlock.ts

@@ -189,6 +189,7 @@ export default class EachBlock extends Node {
 
 		if (this.else) {
 			const each_block_else = compiler.getUniqueName(`${each}_else`);
+			const mountOrIntro = (this.else.block.hasIntroMethod || this.else.block.hasOutroMethod) ? 'i' : 'm';
 
 			block.builders.init.addLine(`var ${each_block_else} = null;`);
 

src/compile/nodes/ElseBlock.ts

@@ -5,6 +5,7 @@ import mapChildren from './shared/mapChildren';
 export default class ElseBlock extends Node {
 	type: 'ElseBlock';
 	children: Node[];
+	block: Block;
 
 	constructor(compiler, parent, scope, info) {
 		super(compiler, parent, scope, info);

test/runtime/samples/each-block-else-mount-or-intro/Widget.html

@@ -0,0 +1 @@
+Foo

test/runtime/samples/each-block-else-mount-or-intro/_config.js

@@ -0,0 +1,5 @@
+export default {
+	nestedTransitions: true,
+	data: { items: [] },
+	html: `No items.`,
+};

test/runtime/samples/each-block-else-mount-or-intro/main.html

@@ -0,0 +1,9 @@
+{#each items as item}
+	<Widget {item}/>
+{:else}
+	No items.
+{/each}
+
+<script>
+	export default { components: { Widget: './Widget.html' } };
+</script>