fix (kotlin): textobj for bodyless class (#748)

In Kotlin data classes, the body is optional, 
This makes `@class.outer` work in those cases

Author: alphashuro

queries/kotlin/textobjects.scm

@@ -2,7 +2,7 @@
   [
     (class_body)
     (enum_class_body)
-  ] @class.inner) @class.outer
+  ]? @class.inner) @class.outer
 
 [
   (function_declaration