add missing prepareForWrite() calls

idea/idea-core/src/org/jetbrains/kotlin/idea/core/overrideImplement/OverrideImplementMembersHandler.kt

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.idea.core.overrideImplement
 
+import com.intellij.codeInsight.FileModificationService
 import com.intellij.codeInsight.hint.HintManager
 import com.intellij.ide.util.MemberChooser
 import com.intellij.lang.LanguageCodeInsightActionHandler
@@ -66,6 +67,8 @@ abstract class OverrideImplementMembersHandler : LanguageCodeInsightActionHandle
         val elementAtCaret = file.findElementAt(editor.caretModel.offset)
         val classOrObject = elementAtCaret?.getNonStrictParentOfType<KtClassOrObject>() ?: return
 
+        if (!FileModificationService.getInstance().prepareFileForWrite(file)) return
+
         val members = collectMembersToGenerate(classOrObject)
         if (members.isEmpty() && !implementAll) {
             HintManager.getInstance().showErrorHint(editor, getNoMembersFoundHint())