KT-1955 Half a file is red on incomplete code

#KT-1955 fixed

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java

@@ -252,7 +252,7 @@ public interface Errors {
                                                    JetBlockExpression blockExpression = (JetBlockExpression)bodyExpression;
                                                    TextRange lastBracketRange = blockExpression.getLastBracketRange();
                                                    if (lastBracketRange == null) {
-                                                       return markElement(element);
+                                                       return Collections.emptyList();
                                                    }
                                                    return markRange(lastBracketRange);
                                                }

compiler/testData/diagnostics/tests/incompleteCode/kt1955.jet

@@ -0,0 +1,8 @@
+//KT-1955 Half a file is red on incomplete code
+
+package b
+
+fun foo() {
+    val <!UNUSED_VARIABLE!>a<!> = 1<!SYNTAX!><!>
+
+