Add an assert in pager.c to confirm that pPager->tempFile is always true

for in-memory databases.

FossilOrigin-Name: 3fd71092063bf1d30e03cf2497ea9c57b3ec82eb

src/pager.c

@@ -6831,6 +6831,7 @@ int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
   /* In order to be able to rollback, an in-memory database must journal
   ** the page we are moving from.
   */
+  assert( pPager->tempFile || !MEMDB );
   if( pPager->tempFile ){
     rc = sqlite3PagerWrite(pPg);
     if( rc ) return rc;