Check if the parent of class has an empty constr before expanding SAM

[KacperFKorban]

Expanding a SAM into an anonymous class assumes that the parent class
has a constructor with an empty parameter list. Before this change, a
situation in which there was no such constructor caused a crash.

fixes #15855

[KacperFKorban]

Looks like there's a case that I missed, converting to draft for now.

[sjrd]

These are things that Scala 2 can handle correctly, filling in the appropriate Nil or default value:

$ cs launch scala:2.13.8
Welcome to Scala 2.13.8 (OpenJDK 64-Bit Server VM, Java 1.8.0_342).
Type in expressions for evaluation. Or try :help.

scala> class MyFunction(val args: String*)
class MyFunction

scala> trait MyFun[+R] extends MyFunction { def apply(i: Int): R }
trait MyFun

scala> val f: MyFun[Int] = _ + 1
val f: MyFun[Int] = $anonfun$1@2728add3

scala> f(5)
val res1: Int = 6

scala> f.args
val res2: Seq[String] = List()

scala> class MyFunction(val arg: String = "foo")
class MyFunction

scala> trait MyFun[+R] extends MyFunction { def apply(i: Int): R }
trait MyFun

scala> val f: MyFun[Int] = _ + 1
val f: MyFun[Int] = $anonfun$1@2f1b8770

scala> f(5)
val res3: Int = 6

scala> f.arg
val res4: String = foo

[KacperFKorban]

@sjrd Right, I see. Then the fix is going to be entirely different then. Will open a new PR for it then.