Fixed keeping of folded state for imports on optimize

idea/src/org/jetbrains/kotlin/idea/imports/KotlinImportOptimizer.kt

@@ -149,14 +149,17 @@ public class KotlinImportOptimizer() : ImportOptimizer {
             //TODO: do not touch file if everything is already correct?
 
             ApplicationManager.getApplication()!!.runWriteAction(Runnable {
-                for (import in file.getImportDirectives()) {
-                    import.delete()
-                }
+                // remove old imports after adding new ones to keep imports folding state
+                val oldImports = file.getImportDirectives()
 
                 val importList = file.getImportList()!!
                 val psiFactory = JetPsiFactory(file.getProject())
                 for (importPath in sortedImportsToGenerate) {
-                    importList.add(psiFactory.createImportDirective(importPath))
+                    importList.addBefore(psiFactory.createImportDirective(importPath), oldImports.lastOrNull()) // insert into the middle to keep collapsed state
+                }
+
+                for (import in oldImports) {
+                    import.delete()
                 }
             })
         }