Stop crash on multiple attachment selected

Fixed #5272
Closes #5440
// FREEBIE

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -1059,6 +1059,7 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
   }
 
   private void setMedia(Uri uri, MediaType mediaType) {
+    if (uri == null) return;
     attachmentManager.setMedia(masterSecret, uri, mediaType, getCurrentMediaConstraints());
   }
 

src/org/thoughtcrime/securesms/util/MediaUtil.java

@@ -72,6 +72,8 @@ public class MediaUtil {
   }
 
   public static @Nullable String getMimeType(Context context, Uri uri) {
+    if (uri == null) return null;
+
     if (PersistentBlobProvider.isAuthority(context, uri)) {
       return PersistentBlobProvider.getMimeType(context, uri);
     }