Extract Function: Fix NPE caused by unmatched offset-to-reference maps

#KT-5001 Fixed

idea/src/org/jetbrains/jet/plugin/refactoring/extractFunction/extractFunctionUtils.kt

@@ -739,7 +739,7 @@ fun ExtractionDescriptor.generateFunction(
                 body.getStatements().last?.let {
                     val newExpr = it.replaced(JetPsiFactory.createReturn(project, it.getText() ?: throw AssertionError("Return expression shouldn't be empty: code fragment = ${body.getText()}"))).getReturnedExpression()!!
                     val counterpartMap = createNameCounterpartMap(it, newExpr)
-                    nameByOffset.entrySet().forEach { it.setValue(counterpartMap[it.getValue()]!!) }
+                    nameByOffset.entrySet().forEach { e -> counterpartMap[e.getValue()]?.let { e.setValue(it) } }
                 }
         }
     }

idea/testData/refactoring/extractFunction/parameters/misc/kt5001.kt

@@ -0,0 +1,12 @@
+fun Int.bar(n: Int): Boolean {
+    return true
+}
+
+// SIBLING:
+fun main(args: Array<String>) {
+    val t = if (args.size > 0) {
+        <selection>val al = 0
+        al.bar(1)</selection>
+    }
+    else false
+}

idea/testData/refactoring/extractFunction/parameters/misc/kt5001.kt.after

@@ -0,0 +1,16 @@
+fun Int.bar(n: Int): Boolean {
+    return true
+}
+
+// SIBLING:
+fun main(args: Array<String>) {
+    val t = if (args.size > 0) {
+        b()
+    }
+    else false
+}
+
+fun b(): Boolean {
+    val al = 0
+    return al.bar(1)
+}

idea/tests/org/jetbrains/jet/plugin/refactoring/introduce/introduceVariable/JetExtractionTestGenerated.java

@@ -724,6 +724,11 @@ public class JetExtractionTestGenerated extends AbstractJetExtractionTest {
                     doExtractFunctionTest("idea/testData/refactoring/extractFunction/parameters/misc/innerClassObject.kt");
                 }
                 
+                @TestMetadata("kt5001.kt")
+                public void testKt5001() throws Exception {
+                    doExtractFunctionTest("idea/testData/refactoring/extractFunction/parameters/misc/kt5001.kt");
+                }
+                
                 @TestMetadata("multiDeclaration.kt")
                 public void testMultiDeclaration() throws Exception {
                     doExtractFunctionTest("idea/testData/refactoring/extractFunction/parameters/misc/multiDeclaration.kt");