improve corrupt db detection and handling part of fix for 48466 r=mscott

mailnews/db/msgdb/src/nsImapMailDatabase.cpp

@@ -93,7 +93,7 @@ NS_IMETHODIMP nsImapMailDatabase::Open(nsIFileSpec *aFolderName, PRBool create,
 	
 	err = mailDB->OpenMDB((const char *) summarySpec, create);
 
-	if (NS_SUCCEEDED(err))
+	if (err == NS_OK)
 	{
 		mailDB->GetDBFolderInfo(&folderInfo);
 		if (folderInfo == NULL)
@@ -131,7 +131,9 @@ NS_IMETHODIMP nsImapMailDatabase::Open(nsIFileSpec *aFolderName, PRBool create,
 		else if (err != NS_OK)
 		{
 			*pMessageDB = NULL;
+      mailDB->Close(PR_FALSE);
 			delete mailDB;
+      summarySpec.Delete(PR_FALSE);  // blow away the db if it's corrupt.
 			mailDB = NULL;
 		}
 	}

mailnews/db/msgdb/src/nsMsgDatabase.cpp

@@ -916,7 +916,8 @@ NS_IMETHODIMP nsMsgDatabase::OpenMDB(const char *dbName, PRBool create)
 				}
 				while (NS_SUCCEEDED(ret) && !outBroken && !outDone);
 //				m_mdbEnv->ClearErrors(); // ### temporary...
-				if (NS_SUCCEEDED(ret) && outDone)
+        // only 0 is a non-error return.
+				if (ret == 0 && outDone)
 				{
 					ret = myMDBFactory->ThumbToOpenStore(m_mdbEnv, thumb, &m_mdbStore);
 					if (ret == NS_OK && m_mdbStore)