[fix](auth)fix external catalog cannot use db (#16269)

Author: zddr

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

@@ -78,7 +78,9 @@ public void analyze(Analyzer analyzer) throws AnalysisException, UserException {
         }
         database = ClusterNamespace.getFullName(getClusterName(), database);
 
-        if (!Env.getCurrentEnv().getAuth().checkDbPriv(ConnectContext.get(), database, PrivPredicate.SHOW)) {
+        if (!Env.getCurrentEnv().getAuth()
+                .checkDbPriv(ConnectContext.get(), ConnectContext.get().getDefaultCatalog(), database,
+                        PrivPredicate.SHOW)) {
             ErrorReport.reportAnalysisException(ErrorCode.ERR_DBACCESS_DENIED_ERROR,
                     analyzer.getQualifiedUser(), database);
         }

fe/fe-core/src/main/java/org/apache/doris/catalog/Env.java

@@ -4392,7 +4392,7 @@ public void changeCatalog(ConnectContext ctx, String catalogName) throws DdlExce
 
     // Change current database of this session.
     public void changeDb(ConnectContext ctx, String qualifiedDb) throws DdlException {
-        if (!auth.checkDbPriv(ctx, qualifiedDb, PrivPredicate.SHOW)) {
+        if (!auth.checkDbPriv(ctx, ctx.getDefaultCatalog(), qualifiedDb, PrivPredicate.SHOW)) {
             ErrorReport.reportDdlException(ErrorCode.ERR_DBACCESS_DENIED_ERROR, ctx.getQualifiedUser(), qualifiedDb);
         }
 

fe/fe-core/src/test/java/org/apache/doris/mysql/privilege/MockedAuth.java

@@ -36,6 +36,10 @@ public static void mockedAuth(PaloAuth auth) {
                 minTimes = 0;
                 result = true;
 
+                auth.checkDbPriv((ConnectContext) any, anyString, anyString, (PrivPredicate) any);
+                minTimes = 0;
+                result = true;
+
                 auth.checkTblPriv((ConnectContext) any, anyString, anyString, (PrivPredicate) any);
                 minTimes = 0;
                 result = true;