[android] re-create renderer on surface update after app backgrounding (in case egl context is preserved, but surface is not)

platform/android/src/map_renderer.cpp

@@ -184,7 +184,12 @@ void MapRenderer::onSurfaceCreated(JNIEnv&) {
     }
 }
 
-void MapRenderer::onSurfaceChanged(JNIEnv&, jint width, jint height) {
+void MapRenderer::onSurfaceChanged(JNIEnv& env, jint width, jint height) {
+    if (!renderer) {
+        // In case the surface has been destroyed (due to app back-grounding)
+        onSurfaceCreated(env);
+    }
+
     backend->resizeFramebuffer(width, height);
     framebufferSizeChanged = true;
     requestRender();

platform/android/src/map_renderer.hpp

@@ -94,7 +94,9 @@ private:
 
     void onSurfaceChanged(JNIEnv&, jint width, jint height);
 
-    // Called on Main thread
+private:
+    // Called on either Main or GL thread //
+
     void onSurfaceDestroyed(JNIEnv&);
 
 private: