KT-12942 related: remove braces now does not work for if inside if

(cherry picked from commit c1faed5)

idea/src/org/jetbrains/kotlin/idea/intentions/RemoveBracesIntention.kt

@@ -23,9 +23,10 @@ import org.jetbrains.kotlin.psi.*
 
 class RemoveBracesIntention : SelfTargetingIntention<KtBlockExpression>(KtBlockExpression::class.java, "Remove braces") {
     override fun isApplicableTo(element: KtBlockExpression, caretOffset: Int): Boolean {
-        if (element.statements.size != 1) return false
+        val singleStatement = element.statements.singleOrNull() ?: return false
 
         val containerNode = element.parent as? KtContainerNode ?: return false
+        if (singleStatement is KtIfExpression && containerNode.parent is KtIfExpression) return false
 
         val lBrace = element.lBrace ?: return false
         val rBrace = element.rBrace ?: return false

idea/testData/intentions/removeBraces/ifInsideIf.kt

@@ -0,0 +1,11 @@
+// IS_APPLICABLE: false
+fun test(b: Boolean): String {
+    if (b == true) {
+        if (true) return "first"
+    }<caret>
+    else if (b == false) {
+        if (true) return "second"
+    }
+
+    return "none"
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -7697,6 +7697,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("ifInsideIf.kt")
+        public void testIfInsideIf() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/removeBraces/ifInsideIf.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("ifWithComment.kt")
         public void testIfWithComment() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/removeBraces/ifWithComment.kt");