fix(core registry): Do nothing with Patterns without a trigger.

Patterns without a trigger broke the registry scan method. Now they don't.

src/core/registry.js

@@ -174,9 +174,22 @@ const registry = {
             }
         }
 
+        // Clean up selectors:
+        // - Remove whitespace,
+        // - Remove trailing commas,
+        // - Join to selecto string.
+        const selector_string = selectors.map(
+            (selector) => selector.trim().replace(/,$/, "")
+        ).join(",");
+
+        // Exit, if no selector.
+        if (!selector_string) {
+            return;
+        }
+
         let matches = dom.querySelectorAllAndMe(
             content,
-            selectors.map((it) => it.trim().replace(/,$/, "")).join(",")
+            selector_string
         );
         matches = matches.filter((el) => {
             // Filter out patterns:

src/core/registry.test.js

@@ -104,4 +104,16 @@ describe("pat-registry: The registry for patterns", function () {
 
         done();
     });
+
+    it("Does nothing with Patterns without a trigger.", function () {
+        registry.register(
+            {
+                name: "pattern-without-trigger"
+            }
+        )
+
+        const el = document.createElement("div");
+        expect(() => { registry.scan(el) }).not.toThrow(DOMException);
+    });
+
 });