[shotwell] Clear ACDSEE tag transformer

[Jens Georg <jensgeorg src gnome org>]

commit 5d2ddea6fc200c65af21e387bf2938078d89ec4b
Author: Jens Georg <mail jensge org>
Date:   Fri Feb 22 21:29:04 2019 +0100

    Clear ACDSEE tag transformer
    
    The transformer was only created once, but the result variable wasn't
    cleared between calls, thus piling up the tags from all images
    
    Fixes #89
    Fixes #75

 src/photos/PhotoMetadata.vala | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/photos/PhotoMetadata.vala b/src/photos/PhotoMetadata.vala
index 9414cd76..74dc5591 100644
--- a/src/photos/PhotoMetadata.vala
+++ b/src/photos/PhotoMetadata.vala
@@ -70,6 +70,8 @@ public class ACDSeeKeywordTransformer : KeywordTransformer {
     }
 
     public override Gee.List<string> transform (string input) throws Error {
+        this.stack.clear();
+        this.result.clear();
         var ctx = new MarkupParseContext (this.parser, 0, this, null);
 
         ctx.parse (input, input.length);