camera2 ndk: unlock metadata in case of error

Change-Id: Ic0790127c6ba4a6ab3d4de8d974725b58d6370c2
diff --git a/camera/ndk/impl/ACameraMetadata.cpp b/camera/ndk/impl/ACameraMetadata.cpp
index 631f6cd..895514e 100644
--- a/camera/ndk/impl/ACameraMetadata.cpp
+++ b/camera/ndk/impl/ACameraMetadata.cpp
@@ -426,6 +426,7 @@
             camera_metadata_ro_entry_t entry;
             int ret = get_camera_metadata_ro_entry(rawMetadata, i, &entry);
             if (ret != 0) {
+                mData->unlock(rawMetadata);
                 ALOGE("%s: error reading metadata index %zu", __FUNCTION__, i);
                 return ACAMERA_ERROR_UNKNOWN;
             }