Check nullability in initial constraints

except constraints for receiver type (it can be accessed via safe call)

core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt

@@ -41,6 +41,7 @@ import org.jetbrains.kotlin.types.checker.TypeCheckingProcedureCallbacks
 import org.jetbrains.kotlin.types.typeUtil.builtIns
 import org.jetbrains.kotlin.types.typeUtil.getNestedArguments
 import org.jetbrains.kotlin.types.typeUtil.isDefaultBound
+import org.jetbrains.kotlin.types.typeUtil.makeNotNullable
 import java.util.*
 
 public class ConstraintSystemImpl : ConstraintSystem {
@@ -474,15 +475,19 @@ public class ConstraintSystemImpl : ConstraintSystem {
     }
 
     private fun satisfyInitialConstraints(): Boolean {
-        fun JetType.substituteAndMakeNullable(): JetType? {
+        fun JetType.substitute(): JetType? {
             val substitutor = getSubstitutor(substituteOriginal = false) { TypeProjectionImpl(ErrorUtils.createUninferredParameterType(it)) }
-            val result = substitutor.substitute(this, Variance.INVARIANT) ?: return null
-            return TypeUtils.makeNullable(result)
+            return substitutor.substitute(this, Variance.INVARIANT) ?: return null
         }
         return initialConstraints.all {
-            val resultSubType = it.subtype.substituteAndMakeNullable() ?: return false
-            val resultSuperType = it.superType.substituteAndMakeNullable() ?: return false
-            when (it.kind) {
+            constraint ->
+            val resultSubType = constraint.subtype.substitute()?.let {
+                // the call might be done via safe access, so we check for notNullable receiver type;
+                // 'unsafe call' error is reported otherwise later
+                if (constraint.position.kind != ConstraintPositionKind.RECEIVER_POSITION) it else it.makeNotNullable()
+            } ?: return false
+            val resultSuperType = constraint.superType.substitute() ?: return false
+            when (constraint.kind) {
                 SUB_TYPE -> JetTypeChecker.DEFAULT.isSubtypeOf(resultSubType, resultSuperType)
                 EQUAL -> JetTypeChecker.DEFAULT.equalTypes(resultSubType, resultSuperType)
             }