Fix check of constructor params

`ImplicitFunctionN` does not have constructors

Author: liufengyun

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4516,9 +4516,11 @@ object Types {
         def zeroParams(tp: Type): Boolean = tp.stripPoly match {
           case mt: MethodType => mt.paramInfos.isEmpty && !mt.resultType.isInstanceOf[MethodType]
           case et: ExprType => true
-          case _ => false
+          case tp => false
         }
-        if (zeroParams(tp.cls.primaryConstructor.info)) tp
+        // `ImplicitFunctionN` does not have constructors
+        val ctor = tp.cls.primaryConstructor
+        if (!ctor.exists || zeroParams(ctor.info)) tp
         else NoType
       case tp: AppliedType =>
         zeroParamClass(tp.superType)