Cannot transform to flatMap if old working variable used in the nested loop

idea/src/org/jetbrains/kotlin/idea/intentions/loopToCallChain/sequence/FlatMapTransformation.kt

@@ -64,12 +64,14 @@ class FlatMapTransformation(
             val iterableType = FuzzyType(builtIns.iterableType, builtIns.iterable.declaredTypeParameters)
             if (iterableType.checkIsSuperTypeOf(nestedSequenceType) == null) return null
 
+            val nestedLoopBody = nestedLoop.body ?: return null
+            if (state.workingVariable.hasUsages(listOf(nestedLoopBody))) return null // workingVariable is still needed - cannot transform
+
             val newWorkingVariable = nestedLoop.loopParameter ?: return null
-            val loopBody = nestedLoop.body ?: return null
             val transformation = FlatMapTransformation(state.workingVariable, transform)
             val newState = state.copy(
                     innerLoop = nestedLoop,
-                    statements = listOf(loopBody),
+                    statements = listOf(nestedLoopBody),
                     workingVariable = newWorkingVariable
             )
             return SequenceTransformationMatch(transformation, newState)

idea/testData/intentions/loopToCallChain/flatMap_workingVarStillNeeded.kt

@@ -0,0 +1,10 @@
+// WITH_RUNTIME
+// IS_APPLICABLE: false
+fun foo(list: List<String>): String? {
+    <caret>for (s in list) {
+        for (line in s.lines()) {
+            if (line.isNotBlank() && line.length < s.length / 10) return line
+        }
+    }
+    return null
+}