Java: Don't offer "Unwrap 'else' branch" intention if it might cause unreachable code (IDEA-165428)

java/java-tests/testData/codeInsight/unwrapElseBranch/afterChainedIf3.java

@@ -0,0 +1,13 @@
+// "Unwrap 'else' branch" "true"
+
+class T {
+    String f(boolean a, boolean b) {
+        if (a) {
+            if (b) {
+                return "When true";
+            }
+            return "Otherwise";
+        }
+        return "Default";
+    }
+}