fix: print `{#await}` blocks that only have a pending branch (#18908)

.changeset/print-await-pending-only.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: print `{#await}` blocks that only have a pending branch

packages/svelte/src/compiler/print/index.js

@@ -754,7 +754,9 @@ const svelte_visitors = (comments, state) => ({
 		if (node.pending) {
 			context.write('}');
 			block(context, node.pending, state.preserve_whitespace > 0);
-			context.write('{:');
+			if (node.then || node.catch) {
+				context.write('{:');
+			}
 		} else {
 			context.write(' ');
 		}

packages/svelte/tests/print/samples/await-block/input.svelte

@@ -34,3 +34,7 @@
 {:catch}
 	<p>Something went wrong</p>
 {/await}
+
+{#await promise}
+	<p>waiting for the promise to resolve...</p>
+{/await}

packages/svelte/tests/print/samples/await-block/output.svelte

@@ -34,3 +34,7 @@
 {:catch}
 	<p>Something went wrong</p>
 {/await}
+
+{#await promise}
+	<p>waiting for the promise to resolve...</p>
+{/await}