fix behaviour for missing attributes in utterances

Change-Id: Ia2bd6bdce3e470fe74f8405958d89936eb1955c9
diff --git a/lib/KorAP/XML/Annotation/DeReKo/Structure.pm b/lib/KorAP/XML/Annotation/DeReKo/Structure.pm
index 33e9af7..0352ff9 100644
--- a/lib/KorAP/XML/Annotation/DeReKo/Structure.pm
+++ b/lib/KorAP/XML/Annotation/DeReKo/Structure.pm
@@ -118,7 +118,7 @@
 
           my $data;
           foreach (@$attrs) {
-            $data = $_->{'#text'};
+            $data = $_->{'#text'} or next;
 
             $data =~ s/</&lt;/g;
             $data =~ s/>/&gt;/g;
diff --git a/t/real/corpus/KTC/001/000001/struct/structure.xml b/t/real/corpus/KTC/001/000001/struct/structure.xml
index 45ae611..78be0ed 100644
--- a/t/real/corpus/KTC/001/000001/struct/structure.xml
+++ b/t/real/corpus/KTC/001/000001/struct/structure.xml
@@ -189,7 +189,7 @@
           <fs type="attr">
             <f name="who">Mai Thi Nguyen-Kim</f>
             <f name="start">0:00</f>
-            <f name="end">01:20</f>
+            <f name="end"></f>
           </fs>
         </f>
       </fs>
@@ -1894,4 +1894,4 @@
       </fs>
     </span>
   </spanList>
-</layer>
\ No newline at end of file
+</layer>