android: camera_metadata: Add defaul constructor

Add a default constructor that initializes a non valid CameraMetadata
to allow embedding instances of the class in other types.

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/android/camera_metadata.cpp

@@ -13,6 +13,11 @@ using namespace libcamera;
 
 LOG_DEFINE_CATEGORY(CameraMetadata)
 
+CameraMetadata::CameraMetadata()
+	: metadata_(nullptr), valid_(false)
+{
+}
+
 CameraMetadata::CameraMetadata(size_t entryCapacity, size_t dataCapacity)
 {
 	metadata_ = allocate_camera_metadata(entryCapacity, dataCapacity);