Show error if loading file fails

Change-Id: Ic861e199e085db2c455cf883906636d304efde07
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/src/main/java/com/googlesource/gerrit/plugins/imagare/client/UploadByFileSelection.java b/src/main/java/com/googlesource/gerrit/plugins/imagare/client/UploadByFileSelection.java
index 8c78e66..6179784 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/imagare/client/UploadByFileSelection.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/imagare/client/UploadByFileSelection.java
@@ -48,6 +48,8 @@
           }
         }
         r.readAsDataURL(f);
+      } else {
+        $wnd.Gerrit.showError('Failed to load file.');
       }
     }
   }-*/;