CppTools: Fix formatting for lambdas with trailing return type

After the arrow, the state is still the same, as now a type is expected.
Only after the opening brace does the actual function start.

Fixes: QTCREATORBUG-18497
Change-Id: I7bf18fbd6907d36f8869af3a78ad617cf0ee9dbb
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cpptools/cppcodeformatter.cpp

@@ -273,7 +273,13 @@ void CodeFormatter::recalculateStateAfter(const QTextBlock &block)
             case T_RBRACKET:    // '[', ']' and '->' can be part of lambda declarator
             case T_LBRACKET:
             case T_ARROW:       break;
-            default:            leave(); continue;
+            default:
+                if (m_tokenIndex > 0 && tokenAt(m_tokenIndex - 1).kind() == T_ARROW) {
+                    break;
+                } else {
+                    leave();
+                    continue;
+                }
             } break;
 
         case lambda_declarator: