block/vvfat: Plug memory leak in read_directory()

Has always been leaky.  Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit b122c3b)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

block/vvfat.c

@@ -787,7 +787,9 @@ static int read_directory(BDRVVVFATState* s, int mapping_index)
 	    s->current_mapping->path=buffer;
 	    s->current_mapping->read_only =
 		(st.st_mode & (S_IWUSR | S_IWGRP | S_IWOTH)) == 0;
-	}
+        } else {
+            g_free(buffer);
+        }
     }
     closedir(dir);