Fix desugaring empty argument blocks in normArgs

Fixes #14699

Author: odersky

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1876,7 +1876,7 @@ trait Applications extends Compatibility {
      *       formal parameter that is a unary function.
      */
     def normArg(alts: List[TermRef], arg: untpd.Tree, idx: Int): untpd.Tree = arg match
-      case Block(Nil, expr) => normArg(alts, expr, idx)
+      case Block(Nil, expr) if !expr.isEmpty => normArg(alts, expr, idx)
       case untpd.Function(args: List[untpd.ValDef] @unchecked, body) =>
 
         // If ref refers to a method whose parameter at index `idx` is a function type,

tests/pos/i14699.scala

@@ -0,0 +1,7 @@
+def always(block: => Unit): Unit = {}
+def always(args: Int*)(block: => Unit): Unit ={}
+
+def test =
+  val x = always{}
+  val xc: Unit = x
+  always(1,2,3) {}