fix issue #792 (#793)

Author: chavacava

rule/redefines-builtin-id.go

@@ -89,6 +89,9 @@ func (w *lintRedefinesBuiltinID) Visit(node ast.Node) ast.Visitor {
 	case *ast.GenDecl:
 		switch n.Tok {
 		case token.TYPE:
+			if len(n.Specs) < 1 {
+				return nil
+			}
 			typeSpec, ok := n.Specs[0].(*ast.TypeSpec)
 			if !ok {
 				return nil

testdata/redefines-builtin-id.go

@@ -29,3 +29,6 @@ var any int // MATCH /redefinition of the built-in type any/
 const any = 1 // MATCH /redefinition of the built-in type any/
 
 var i, copy int // MATCH /redefinition of the built-in function copy/
+
+// issue #792
+type ()