KT-1778 Automatically cast error

#KT-1778 fixed

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/DataFlowUtils.java

@@ -48,7 +48,7 @@ public class DataFlowUtils {
     @NotNull
     public static DataFlowInfo extractDataFlowInfoFromCondition(@Nullable JetExpression condition, final boolean conditionValue, @Nullable final WritableScope scopeToExtend, final ExpressionTypingContext context) {
         if (condition == null) return context.dataFlowInfo;
-        final Ref<DataFlowInfo> result = new Ref<DataFlowInfo>(context.dataFlowInfo);
+        final Ref<DataFlowInfo> result = new Ref<DataFlowInfo>(null);
         condition.accept(new JetVisitorVoid() {
             @Override
             public void visitIsExpression(JetIsExpression expression) {
@@ -148,7 +148,7 @@ public class DataFlowUtils {
         if (result.get() == null) {
             return context.dataFlowInfo;
         }
-        return result.get();
+        return context.dataFlowInfo.and(result.get());
     }
 
     @Nullable

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
+    }
+}