[core] Fix MapSnapshotter build failure on Windows

MSVC implementation of std::promise is buggy and only works with types
that can be default-constructed. To avoid a compilation failure in the
instantiation of ask() inside MapSnapshotter::getRegion(), which creates
a std::promise<LanLngBounds>, make LatLngBounds' default constructor
public.

2 files changed, 4 insertions, 8 deletions

diff --git a/src/mbgl/map/transform.cpp b/src/mbgl/map/transform.cpp
index e88bb5465c..6b44e633d9 100644
--- a/src/mbgl/map/transform.cpp
+++ b/src/mbgl/map/transform.cpp
@@ -83,14 +83,14 @@ void Transform::jumpTo(const CameraOptions& camera) {
  */
 void Transform::easeTo(const CameraOptions& camera, const AnimationOptions& animation) {
     Duration duration = animation.duration.value_or(Duration::zero());
-    if (state.bounds == LatLngBounds::unbounded() && !isGestureInProgress() && duration != Duration::zero()) {
+    if (state.bounds == LatLngBounds() && !isGestureInProgress() && duration != Duration::zero()) {
         // reuse flyTo, without exaggerated animation, to achieve constant ground speed.
         return flyTo(camera, animation, true);
     }
     const EdgeInsets& padding = camera.padding.value_or(state.edgeInsets);
     LatLng startLatLng = getLatLng(LatLng::Unwrapped);
     const LatLng& unwrappedLatLng = camera.center.value_or(startLatLng);
-    const LatLng& latLng = state.bounds != LatLngBounds::unbounded() ? unwrappedLatLng : unwrappedLatLng.wrapped();
+    const LatLng& latLng = state.bounds != LatLngBounds() ? unwrappedLatLng : unwrappedLatLng.wrapped();
     double zoom = camera.zoom.value_or(getZoom());
     double bearing = camera.bearing ? -*camera.bearing * util::DEG2RAD : getBearing();
     double pitch = camera.pitch ? *camera.pitch * util::DEG2RAD : getPitch();
@@ -102,7 +102,7 @@ void Transform::easeTo(const CameraOptions& camera, const AnimationOptions& anim
         return;
     }
 
-    if (state.bounds == LatLngBounds::unbounded()) {
+    if (state.bounds == LatLngBounds()) {
         if (isGestureInProgress()) {
             // If gesture in progress, we transfer the wrap rounds from the end longitude into
             // start, so the "scroll effect" of rounding the world is the same while assuring the
diff --git a/src/mbgl/map/transform_state.cpp b/src/mbgl/map/transform_state.cpp
index 61007422cb..f3cd8c3886 100644
--- a/src/mbgl/map/transform_state.cpp
+++ b/src/mbgl/map/transform_state.cpp
@@ -10,11 +10,7 @@
 namespace mbgl {
 
 TransformState::TransformState(ConstrainMode constrainMode_, ViewportMode viewportMode_)
-    : bounds(LatLngBounds::unbounded())
-    , constrainMode(constrainMode_)
-    , viewportMode(viewportMode_)
-{
-}
+    : bounds(LatLngBounds()), constrainMode(constrainMode_), viewportMode(viewportMode_) {}
 
 #pragma mark - Matrix