[shotwell/shotwell-0.30] Prevent critical when there is no meta-data

[Jens Georg <jensgeorg src gnome org>]

commit ae1bc707c5ff0ae67ec62b19ecf358d15cd9b4a2
Author: Jens Georg <mail jensge org>
Date:   Tue Sep 11 23:08:13 2018 +0200

    Prevent critical when there is no meta-data

 src/Photo.vala | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/src/Photo.vala b/src/Photo.vala
index c317714e..0d8e955d 100644
--- a/src/Photo.vala
+++ b/src/Photo.vala
@@ -4698,7 +4698,7 @@ public class LibraryPhotoSourceCollection : MediaSourceCollection {
         Gee.HashMultiMap<Tag, LibraryPhoto> map = new Gee.HashMultiMap<Tag, LibraryPhoto>();
         foreach (MediaSource media in media_sources) {
             LibraryPhoto photo = (LibraryPhoto) media;
-            PhotoMetadata metadata = photo.get_metadata();
+            PhotoMetadata? metadata = photo.get_metadata();
             
             // get an index of all the htags in the application
             HierarchicalTagIndex global_index = HierarchicalTagIndex.get_global_index();
@@ -4709,7 +4709,7 @@ public class LibraryPhotoSourceCollection : MediaSourceCollection {
             // hierarchical tag information as plain old tags. If a tag name appears as part of
             // a hierarchical path, it needs to be excluded from being processed as a flat tag
             HierarchicalTagIndex? htag_index = null;
-            if (metadata.has_hierarchical_keywords()) {
+            if (metadata != null && metadata.has_hierarchical_keywords()) {
                 htag_index = HierarchicalTagUtilities.process_hierarchical_import_keywords(
                     metadata.get_hierarchical_keywords());
             }
@@ -4732,7 +4732,7 @@ public class LibraryPhotoSourceCollection : MediaSourceCollection {
                 }
             }
             
-            if (metadata.has_hierarchical_keywords()) {
+            if (metadata != null && metadata.has_hierarchical_keywords()) {
                 foreach (string path in htag_index.get_all_paths()) {
                     string? name = Tag.prep_tag_name(path);
                     if (name != null)