Avoid checking purity of Apply without symbols (#16221)

Author: dwijnand

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -512,7 +512,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
       sym.owner.isPrimitiveValueClass
       || sym.owner == defn.StringClass
       || defn.pureMethods.contains(sym)
-    tree.tpe.isInstanceOf[ConstantType] && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
+    tree.tpe.isInstanceOf[ConstantType] && tree.symbol != NoSymbol && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
     || fn.symbol.isStableMember && !fn.symbol.is(Lazy)  // constructors of no-inits classes are stable
 
   /** The purity level of this reference.

tests/pos/i16174.scala

@@ -0,0 +1,3 @@
+val f = [A] => (a: A) => a
+val x1 = f.apply[Int](4)
+val x2 = f.apply[4](4)