Optimize imports remove reference to get extension function

#KT-3397 Fixed

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetArrayAccessExpression.java

@@ -25,6 +25,7 @@ import com.intellij.psi.PsiReferenceService;
 import com.intellij.psi.impl.source.resolve.reference.ReferenceProvidersRegistry;
 import com.intellij.psi.util.PsiTreeUtil;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.JetNodeTypes;
 import org.jetbrains.jet.lexer.JetTokens;
 
@@ -36,6 +37,14 @@ public class JetArrayAccessExpression extends JetReferenceExpression {
         super(node);
     }
 
+    @Nullable
+    @Override
+    public PsiReference getReference() {
+        PsiReference[] references = getReferences();
+        if (references.length == 1) return references[0];
+        else return null;
+    }
+
     @NotNull
     @Override
     public PsiReference[] getReferences() {

idea/testData/editor/optimizeImports/multifile/ArrayAccessExpression/ArrayAccessExpression_after.kt

@@ -0,0 +1,4 @@
+import test1.MyClass
+import test1.get
+
+val s = MyClass()[1]

idea/testData/editor/optimizeImports/multifile/ArrayAccessExpression/main.kt

@@ -0,0 +1,4 @@
+import test1.MyClass
+import test1.get
+
+val s = MyClass()[1]

idea/testData/editor/optimizeImports/multifile/ArrayAccessExpression/myClass.kt

@@ -0,0 +1,8 @@
+package test1
+
+public class MyClass {
+}
+
+public fun MyClass.get(i: Int): Int {
+    return 1
+}

idea/tests/org/jetbrains/jet/plugin/importOptimizer/OptimizeImportsMultiFileTest.java

@@ -34,6 +34,10 @@ public class OptimizeImportsMultiFileTest extends CodeInsightTestCase {
         doTest(getTestName(false) + "/main.kt", getTestName(false) + "/MyJavaClass.java");
     }
 
+    public void testArrayAccessExpression() throws Exception {
+        doTest(getTestName(false) + "/main.kt", getTestName(false) + "/myClass.kt");
+    }
+
     public void doTest(String... fileNames) throws Exception {
         configureByFiles(null, fileNames);
         invokeFormatFile();