Don't try to read the next start element after the root element

There can only be one root element in an XML document, and when we try
to read another one we get a premature end of document error.

src/plugins/qmljseditor/qmlcodecompletion.cpp

@@ -895,7 +895,7 @@ void QmlCodeCompletion::updateSnippets()
     QFile file(qmlsnippets);
     file.open(QIODevice::ReadOnly);
     QXmlStreamReader xml(&file);
-    while (!xml.atEnd() && xml.readNextStartElement()) {
+    if (xml.readNextStartElement()) {
         if (xml.name() == QLatin1String("snippets")) {
             while (xml.readNextStartElement()) {
                 if (xml.name() == QLatin1String("snippet")) {
@@ -919,7 +919,6 @@ void QmlCodeCompletion::updateSnippets()
                             item.icon = icon;
                             m_snippets.append(item);
                             break;
-
                         }
 
                         if (xml.isCharacters())
@@ -933,14 +932,17 @@ void QmlCodeCompletion::updateSnippets()
                                 data += QChar::ObjectReplacementCharacter;
                             }
                         }
-
-                    }
+                    }
+                } else {
+                    xml.skipCurrentElement();
                 }
             }
+        } else {
+            xml.skipCurrentElement();
         }
     }
     if (xml.hasError())
-        qWarning() << qmlsnippets << xml.errorString();
+        qWarning() << qmlsnippets << xml.errorString() << xml.lineNumber() << xml.columnNumber();
     file.close();
 }