Avoid crash after StopMacroExpansion

When a splice throws a StopMacroExpansion, it's replaced by an
EmptyTree, which has NoType.  Which means you can't cast it, as you
can't call .asInstanceOf on it.  So handle this before calling
ensureConforms.

[Cherry-picked 44aa3c6]

Author: dwijnand

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -449,14 +449,14 @@ object Inlines:
 
       // Take care that only argument bindings go into `bindings`, since positions are
       // different for bindings from arguments and bindings from body.
-      val res = tpd.Inlined(call, bindings, expansion)
+      val inlined = tpd.Inlined(call, bindings, expansion)
 
-      if !hasOpaqueProxies then res
+      if !hasOpaqueProxies || !inlined.tpe.exists then inlined
       else
         val target =
-          if inlinedMethod.is(Transparent) then call.tpe & res.tpe
+          if inlinedMethod.is(Transparent) then call.tpe & inlined.tpe
           else call.tpe
-        res.ensureConforms(target)
+        inlined.ensureConforms(target)
           // Make sure that the sealing with the declared type
           // is type correct. Without it we might get problems since the
           // expression's type is the opaque alias but the call's type is

tests/neg-macros/i19851/Macro_1.scala

@@ -0,0 +1,9 @@
+import scala.quoted.*
+
+opaque type Box[A] = Any
+object Box:
+  transparent inline def pack[A]: Nothing => Box[A] = ${ packImpl[A] }
+
+  private def packImpl[A](using Quotes, Type[A]): Expr[Nothing => Box[A]] =
+    import quotes.reflect.*
+    report.errorAndAbort("Not implemented")

tests/neg-macros/i19851/Test_2.scala

@@ -0,0 +1,3 @@
+class Test:
+  def t1: Unit =
+    Box.pack[Int] // error