QmlDesigner.rewriter: crash fix

When pasting or reading in a Component that has no object definition
inside we crashed.

I added an explicit check in the FirstDefinitionFinder.
In the TextToModelMerger we then handle this case.

Task-Nr: QTCREATORBUG-4730
Reviewed-by: Erik Verbruggen

src/plugins/qmldesigner/designercore/filemanager/firstdefinitionfinder.cpp

@@ -54,13 +54,16 @@ FirstDefinitionFinder::FirstDefinitionFinder(const QString &text):
   \arg the offset of the object to search in
   \return the offset of the first object definition
   */
-quint32 FirstDefinitionFinder::operator()(quint32 offset)
+qint32 FirstDefinitionFinder::operator()(quint32 offset)
 {
     m_offset = offset;
     m_firstObjectDefinition = 0;
 
     Node::accept(m_doc->qmlProgram(), this);
 
+    if (!m_firstObjectDefinition)
+        return -1;
+
     return m_firstObjectDefinition->firstSourceLocation().offset;
 }
 

src/plugins/qmldesigner/designercore/filemanager/firstdefinitionfinder.h

@@ -43,7 +43,7 @@ class FirstDefinitionFinder: protected QmlJS::AST::Visitor
 public:
     FirstDefinitionFinder(const QString &text);
 
-    quint32 operator()(quint32 offset);
+    qint32 operator()(quint32 offset);
 
 protected:
     using QmlJS::AST::Visitor::visit;

src/plugins/qmldesigner/designercore/model/texttomodelmerger.cpp

@@ -1397,6 +1397,10 @@ void TextToModelMerger::setupComponent(const ModelNode &node)
     if (componentText.contains("Component")) { //explicit component
         FirstDefinitionFinder firstDefinitionFinder(componentText);
         int offset = firstDefinitionFinder(0);
+        if (offset < 0) {
+            node.variantProperty("__component_data").setValue(QLatin1String(""));
+            return; //No object definition found
+        }
         ObjectLengthCalculator objectLengthCalculator;
         unsigned length;
         if (objectLengthCalculator(componentText, offset, length)) {