Fix SVG detection (#4401)

* Fix SVG detection

* remove unnecessary import

src/misc/check-svg.ts

@@ -0,0 +1,12 @@
+import * as fs from 'fs';
+import * as isSvg from 'is-svg';
+
+export default function(path: string) {
+	try {
+		const size = fs.statSync(path).size;
+		if (size > 1 * 1024 * 1024) return false;
+		return isSvg(fs.readFileSync(path));
+	} catch {
+		return false;
+	}
+}