JS: fix serialization of fileId in case of incremental compilation

js/js.translator/testData/box/incremental/jsModule.kt

@@ -0,0 +1,32 @@
+// EXPECTED_REACHABLE_NODES: 1018
+
+// MODULE: lib
+// FILE: a.kt
+// MODULE_KIND: AMD
+@file:JsModule("foo")
+
+external fun fooF(): String
+
+// FILE: b.kt
+@file:JsModule("bar")
+
+external fun barF(): String
+
+// FILE: c.kt
+// RECOMPILE
+fun dummyF() = "dummy"
+
+// MODULE: main(lib)
+// FILE: main.kt
+// MODULE_KIND: AMD
+
+fun box(): String {
+    val foo = fooF()
+    if (foo != "foo") return "fail1: $foo"
+
+    val bar = barF()
+    if (bar != "bar") return "fail2: $bar"
+
+    return "OK"
+}
+