Kotlin migration: extract data context into a function, check it on null

The extraction itself is needed due to different behaviour of related
IDEA functions in different platforms.
Check on null is needed because `createFromAnAction` last argument
cannot be null, otherwise we will get an exception.

Partial fix of KT-26399

idea/src/org/jetbrains/kotlin/idea/configuration/KotlinMigrationProjectComponent.kt

@@ -5,7 +5,6 @@
 
 package org.jetbrains.kotlin.idea.configuration
 
-import com.intellij.ide.DataManager
 import com.intellij.openapi.actionSystem.ActionManager
 import com.intellij.openapi.actionSystem.ActionPlaces
 import com.intellij.openapi.actionSystem.AnActionEvent
@@ -94,10 +93,12 @@ class KotlinMigrationProjectComponent(val project: Project) {
             if (migrationNotificationDialog.isOK) {
                 val action = ActionManager.getInstance().getAction(CodeMigrationAction.ACTION_ID)
 
-                val dataContext = DataManager.getInstance().dataContextFromFocus.result
-                val actionEvent = AnActionEvent.createFromAnAction(action, null, ActionPlaces.ACTION_SEARCH, dataContext)
+                val dataContext = getDataContextFromDialog(migrationNotificationDialog)
+                if (dataContext != null) {
+                    val actionEvent = AnActionEvent.createFromAnAction(action, null, ActionPlaces.ACTION_SEARCH, dataContext)
 
-                action.actionPerformed(actionEvent)
+                    action.actionPerformed(actionEvent)
+                }
             }
         }
     }

idea/src/org/jetbrains/kotlin/idea/configuration/MigrationUtils.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.configuration
+
+import com.intellij.ide.DataManager
+import com.intellij.openapi.actionSystem.DataContext
+import com.intellij.openapi.ui.DialogWrapper
+
+@Suppress("UNUSED_PARAMETER")
+internal fun getDataContextFromDialog(wrapper: DialogWrapper): DataContext? = DataManager.getInstance().dataContextFromFocus.result