8168774: Polymorhic signature method check crashes javac

Summary: Check for polysig method assumes arity is greater than zero
Reviewed-by: vromero

langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java

@@ -1004,7 +1004,7 @@ public class Types {
        List<Type> argtypes = msym.type.getParameterTypes();
        return (msym.flags_field & NATIVE) != 0 &&
               (msym.owner == syms.methodHandleType.tsym || msym.owner == syms.varHandleType.tsym) &&
-               argtypes.tail.tail == null &&
+               argtypes.length() == 1 &&
                argtypes.head.hasTag(TypeTag.ARRAY) &&
                ((ArrayType)argtypes.head).elemtype.tsym == syms.objectType.tsym;
    }

langtools/test/tools/javac/meth/BadPolySig.java

+/*
+ * @test
+ * @bug 8168774
+ * @summary Polymorhic signature method check crashes javac
+ * @compile -Xmodule:java.base BadPolySig.java
+ */
+
+package java.lang.invoke;
+
+class MethodHandle {
+    native Object m();
+}