[fix](multi-catalog) fix show data on external catalog (#15227)

if switch external catalog, and use a database that has same name with one database of internal catalog,
query 'show data', will get data info from internal catalog.

fe/fe-core/src/main/java/org/apache/doris/analysis/ShowDataStmt.java

@@ -99,6 +99,8 @@ public class ShowDataStmt extends ShowStmt {
             // disallow external catalog
             Util.prohibitExternalCatalog(tableName.getCtl(), this.getClass().getSimpleName());
             dbName = tableName.getDb();
+        } else {
+            Util.prohibitExternalCatalog(analyzer.getDefaultCatalog(), this.getClass().getSimpleName());
         }
 
         Database db = Env.getCurrentInternalCatalog().getDbOrAnalysisException(dbName);