fix JabRef#6127

add concise tips when SaveException happend

Author: chenyuheng

src/main/java/org/jabref/gui/exporter/SaveDatabaseAction.java

@@ -236,7 +236,7 @@ private boolean saveDatabase(Path file, boolean selectedOnly, Charset encoding,
         } catch (UnsupportedCharsetException ex) {
             throw new SaveException(Localization.lang("Character encoding '%0' is not supported.", encoding.displayName()), ex);
         } catch (IOException ex) {
-            throw new SaveException("Problems saving:", ex);
+            throw new SaveException("Problems saving:" + ex, ex);
         }
 
         return true;