KT-1778 Automatically cast error

#KT-1778 fixed

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/kt1778.jet

@@ -0,0 +1,11 @@
+//KT-1778 Automatically cast error
+package kt1778
+
+fun main(args : Array<String>) {
+    val x = args[0]: Any
+    if(x is java.lang.CharSequence) {
+        if ("a" == x) x.length() else x.length() // OK
+        if ("a" == x || "b" == x) x.length() else x.length() // <– THEN ERROR
+        if ("a" == x && "a" == x) x.length() else x.length() // <– ELSE ERROR
+    }
+}