server: Use a better error code for a zero-size mapped file.
diff --git a/server/mapping.c b/server/mapping.c
index c9813f2..af6f074 100644
--- a/server/mapping.c
+++ b/server/mapping.c
@@ -308,7 +308,7 @@
             if (!get_file_size( mapping->file, &size )) goto error;
             if (!size)
             {
-                set_error( STATUS_FILE_INVALID );
+                set_error( STATUS_MAPPED_FILE_SIZE_ZERO );
                 goto error;
             }
         }