Minor: convert to expression body is forbidden also for nested non-exhaustive whens

idea/src/org/jetbrains/kotlin/idea/intentions/Utils.kt

@@ -133,7 +133,7 @@ fun KtExpression.negate(): KtExpression {
 }
 
 fun KtExpression.resultingWhens(): List<KtWhenExpression> = when (this) {
-    is KtWhenExpression -> listOf(this)
+    is KtWhenExpression -> listOf(this) + entries.map { it.expression?.resultingWhens() ?: listOf() }.flatten()
     is KtIfExpression -> (then?.resultingWhens() ?: listOf()) + (`else`?.resultingWhens() ?: listOf())
     is KtBinaryExpression -> (left?.resultingWhens() ?: listOf()) + (right?.resultingWhens() ?: listOf())
     is KtUnaryExpression -> this.baseExpression?.resultingWhens() ?: listOf()

idea/testData/intentions/convertToExpressionBody/whenWhenNonExhaustive.kt

@@ -0,0 +1,18 @@
+// IS_APPLICABLE: false
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) {
+    <caret>when (access) {
+        AccessMode.READ -> when (mode) {
+            true -> println("read")
+            false -> println("noread")
+        }
+        AccessMode.WRITE -> when (mode) {
+            true -> println("write")
+        }
+        AccessMode.RW -> when (mode) {
+            true -> println("both")
+            else -> println("no both")
+        }
+    }
+}
+fun println(s: String) {}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -4960,6 +4960,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("whenWhenNonExhaustive.kt")
+        public void testWhenWhenNonExhaustive() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/whenWhenNonExhaustive.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("while.kt")
         public void testWhile() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/while.kt");