Don't call getLength() on OUStringBuffer after makeStringAndClear()

It's the length of the OUString that we just made from the
OUStringBuffer that we want.

Fixes a problem where the code would try to execute an erronoeus SQL
statement like:

')EATE TABLE "Tasks" ("Notes" VARCHAR(32765),"TaskID" INTEGER,"EndDate" DATE,"StartDate" DATE,"Description" VARCHAR(65000),'

Too lazy to file a bug for this, the error should be obvious by just
reading the code.

Change-Id: I473cd8a7a9791700ca8b6467a84f4bad5dee4d55
Reviewed-on: https://gerrit.libreoffice.org/47230Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

connectivity/source/drivers/firebird/Tables.cxx

@@ -191,7 +191,7 @@ ObjectType Tables::appendObject(const OUString& rName,
     else
     {
         if ( sSql.endsWith(",") )
-            sSql = sSql.replaceAt(aSqlBuffer.getLength()-1, 1, ")");
+            sSql = sSql.replaceAt(sSql.getLength()-1, 1, ")");
         else
             sSql += ")";
     }