Redundant nullable return type: fix false positive with elvis return

#KT-41878 Fixed

idea/testData/inspectionsLocal/redundantNullableReturnType/function/returnNullableInElvis.kt

@@ -0,0 +1,5 @@
+// PROBLEM: none
+fun elvisFun(str: String?): String?<caret> {
+    val v = str?.length ?: return null
+    return v.toString()
+}

idea/testData/inspectionsLocal/redundantNullableReturnType/property/returnNullableInElvis.kt

@@ -0,0 +1,8 @@
+// PROBLEM: none
+val foo: String?<caret>
+    get() {
+        val s = bar() ?: return null
+        return s
+    }
+
+fun bar(): String? = null