Rearrange pre-writing DB checks in DB logger.

Now that the logger is started earlier in startup, the DB logger starts
before the database is configured, so hold all DB access until the
database is ready.

mythtv/libs/libmythbase/mythlogging.cpp

@@ -451,13 +451,16 @@ void DBLoggerThread::run(void)
 bool DatabaseLogger::isDatabaseReady()
 {
     bool ready = false;
-    MythDB *db;
+    MythDB *db = GetMythDB();
 
-    if ( !m_loggingTableExists )
-        m_loggingTableExists = tableExists(m_handle.string);
+    if ((db) && db->HaveValidDatabase())
+    {
+        if ( !m_loggingTableExists )
+            m_loggingTableExists = tableExists(m_handle.string);
 
-    if ( m_loggingTableExists && (db = GetMythDB()) && db->HaveValidDatabase() )
-        ready = true;
+        if ( m_loggingTableExists )
+            ready = true;
+    }
 
     return ready;
 }