FB-01: fix ambient GPS's first fix not correcting the initial zoom-2

Emulator verification caught a real bug the widget tests missed: the
shell background map builds before any location fix has resolved, so
ambientPosition starts null and the initial camera locks at zoom 2.
The first fix to arrive only re-centered (preserving that stale zoom
forever) instead of also jumping to ambientZoom.

test/ride_map_test.dart

@@ -250,6 +250,45 @@ void main() {
       expect(center.longitude, closeTo(fix2.longitude, 1e-9));
     });
 
+    testWidgets('the first ambient fix to arrive after construction corrects the '
+        'zoom, not just the center -- a plain re-center would otherwise leave the '
+        'map at the initial zoom-2 forever', (tester) async {
+      // Reproduces a real device bug found in emulator verification: the shell
+      // background map builds before any location permission/fix has resolved, so
+      // `ambientPosition` starts null and the initial camera locks at zoom 2 (the
+      // `bounds == null` fallback). The first fix to actually arrive must jump to
+      // `ambientZoom`, not just re-center at whatever zoom the map already happens
+      // to be sitting at.
+      const fix = ll.LatLng(51.0, -114.0);
+
+      Widget build(ll.LatLng? ambient) => MaterialApp(
+            theme: ripprTheme(),
+            home: Scaffold(
+              body: RideMap(
+                points: const [],
+                segments: const [],
+                showEmptyLabel: false,
+                follow: true,
+                ambientPosition: ambient,
+              ),
+            ),
+          );
+
+      await tester.pumpWidget(build(null));
+      await tester.pump();
+
+      var map = tester.widget<FlutterMap>(find.byType(FlutterMap));
+      expect(map.mapController!.camera.zoom, 2);
+
+      await tester.pumpWidget(build(fix));
+      await tester.pump();
+
+      map = tester.widget<FlutterMap>(find.byType(FlutterMap));
+      expect(map.mapController!.camera.zoom, ambientZoom);
+      expect(map.mapController!.camera.center.latitude, closeTo(fix.latitude, 1e-9));
+      expect(map.mapController!.camera.center.longitude, closeTo(fix.longitude, 1e-9));
+    });
+
     testWidgets('a manual pan cancels ambient following the same way it cancels '
         'recording-follow', (tester) async {
       const fix1 = ll.LatLng(51.0, -114.0);