format-table: add _TABLE_ERSATZ_INVALID to follow our usual coding style

Closes CID#1609497.

Author: yuwata

src/shared/format-table.h

@@ -86,6 +86,7 @@ typedef enum TableErsatz {
         TABLE_ERSATZ_UNSET,
         TABLE_ERSATZ_NA,
         _TABLE_ERSATZ_MAX,
+        _TABLE_ERSATZ_INVALID = -EINVAL,
 } TableErsatz;
 
 typedef struct Table Table;