Make extra calls to sqlite3_shutdown() be harmless no-ops. (CVS 6520)

FossilOrigin-Name: d80822953c2d2f2fd7f6acdd3caa403c0decacc4
diff --git a/src/main.c b/src/main.c
index 6edaeee..a6cdefb 100644
--- a/src/main.c
+++ b/src/main.c
@@ -14,7 +14,7 @@
 ** other files are for internal use by SQLite and should not be
 ** accessed by users of the library.
 **
-** $Id: main.c,v 1.537 2009/04/17 16:54:23 drh Exp $
+** $Id: main.c,v 1.538 2009/04/19 12:23:58 drh Exp $
 */
 #include "sqliteInt.h"
 
@@ -213,18 +213,22 @@
 ** Undo the effects of sqlite3_initialize().  Must not be called while
 ** there are outstanding database connections or memory allocations or
 ** while any part of SQLite is otherwise in use in any thread.  This
-** routine is not threadsafe.  Not by a long shot.
+** routine is not threadsafe.  But it is safe to invoke this routine
+** on when SQLite is already shut down.  If SQLite is already shut down
+** when this routine is invoked, then this routine is a harmless no-op.
 */
 int sqlite3_shutdown(void){
-  sqlite3GlobalConfig.isMallocInit = 0;
-  sqlite3PcacheShutdown();
   if( sqlite3GlobalConfig.isInit ){
-    sqlite3_os_end();
+    sqlite3GlobalConfig.isMallocInit = 0;
+    sqlite3PcacheShutdown();
+    if( sqlite3GlobalConfig.isInit ){
+      sqlite3_os_end();
+    }
+    sqlite3_reset_auto_extension();
+    sqlite3MallocEnd();
+    sqlite3MutexEnd();
+    sqlite3GlobalConfig.isInit = 0;
   }
-  sqlite3_reset_auto_extension();
-  sqlite3MallocEnd();
-  sqlite3MutexEnd();
-  sqlite3GlobalConfig.isInit = 0;
   return SQLITE_OK;
 }