[Qt] Added QMapboxGL::sourceExists

platform/qt/include/qmapboxgl.hpp

@@ -208,6 +208,7 @@ public:
     QMargins margins() const;
 
     void addSource(const QString &sourceID, const QVariantMap& params);
+    bool sourceExists(const QString &sourceID);
     void updateSource(const QString &sourceID, const QVariantMap& params);
     void removeSource(const QString &sourceID);
 

platform/qt/src/qmapboxgl.cpp

@@ -1243,6 +1243,14 @@ void QMapboxGL::addSource(const QString &id, const QVariantMap &params)
     d_ptr->mapObj->addSource(std::move(*source));
 }
 
+/*!
+    Returns true if the layer with given \a id exists, false otherwise.
+*/
+bool QMapboxGL::sourceExists(const QString& sourceID)
+{
+    return !!d_ptr->mapObj->getSource(sourceID.toStdString());
+}
+
 /*!
     Updates the source \a id with new \a params.