do not run the search if no source is selected

vue/Search/Form.vue

@@ -190,7 +190,7 @@ export default {
     },
     async search () {
       // Run the actual search
-      if (!this.isValid() || this.loading) return
+      if (!this.isValid() || !this.sources.length || this.loading) return
       this.loading = true
       try {
         const payload = this.parsedQuery