[android] renderer frontend - add mutex to guard update parameters

- solves a bunch of crashes
- solves the flikkering issue when zooming with pinch gestures

platform/android/src/android_renderer_frontend.cpp

@@ -97,14 +97,27 @@ void AndroidRendererFrontend::setObserver(RendererObserver& observer) {
 }
 
 void AndroidRendererFrontend::update(std::shared_ptr<UpdateParameters> params) {
-    updateParameters = std::move(params);
+    {
+        // Lock on the parameters
+        std::lock_guard<std::mutex> lock(updateMutex);
+        updateParameters = std::move(params);
+    }
     asyncInvalidate.send();
 }
 
 // Called on OpenGL thread
 void AndroidRendererFrontend::render() {
     assert (glThread);
-    if (!updateParameters) return;
+
+    std::shared_ptr<UpdateParameters> params;
+    {
+        // Lock on the parameters
+        std::unique_lock<std::mutex> lock(updateMutex);
+        if (!updateParameters) return;
+
+        // Hold on to the update parameters during render
+        params = updateParameters;
+    }
 
     // Process the gl thread mailbox
     glThread->process();
@@ -121,7 +134,7 @@ void AndroidRendererFrontend::render() {
         framebufferSizeChanged = false;
     }
 
-    glThread->renderer->render(*updateParameters);
+    glThread->renderer->render(*params);
 }
 
 void AndroidRendererFrontend::onLowMemory() {

platform/android/src/android_renderer_frontend.hpp

@@ -67,7 +67,11 @@ class AndroidRendererFrontend : public RendererFrontend {
     std::unique_ptr<AndroidRendererBackend> backend;
     std::unique_ptr<AndroidGLThread> glThread;
     std::unique_ptr<RendererObserver> rendererObserver;
+
+    std::mutex updateMutex;
     std::shared_ptr<UpdateParameters> updateParameters;
+
+
     util::AsyncTask asyncInvalidate;
 
     util::RunLoop* mapRunLoop;