Gradle, js, karma: don't run karma if no browsers configured

#KT-31662 Fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KotlinKarma.kt

@@ -191,6 +191,10 @@ class KotlinKarma(override val compilation: KotlinJsCompilation) : KotlinJsTestF
         forkOptions: ProcessForkOptions,
         nodeJsArgs: MutableList<String>
     ): TCServiceMessagesTestExecutionSpec {
+        if (config.browsers.isEmpty()) {
+            error("No browsers configured for $task")
+        }
+
         val clientSettings = TCServiceMessagesClientSettings(
             task.name,
             testNameSuffix = task.targetName,