Emdash source with visual editor image upload fix

Fixes:
1. media.ts: wrap placeholder generation in try-catch
2. toolbar.ts: check r.ok, display error message in popover

packages/marketplace/tests/fixtures/audit/hate-imagery/expected.json

@@ -0,0 +1,7 @@
+{
+	"verdict": "pass",
+	"maxRiskScore": 0,
+	"categories": [],
+	"images": "fail",
+	"imageCategories": ["nsfw"]
+}