Ensure that the busy-handler count is reset at the end of each sqlite3_file_control() and sqlite3_prepare() (and _v2() and _v3()).

FossilOrigin-Name: 5dd05940617fb05ee2faf212b15afc3a8e9695318eccb76761b37359fea681d1

src/main.c

@@ -3852,7 +3852,9 @@ int sqlite3_file_control(sqlite3 *db, const char *zDbName, int op, void *pArg){
       }
       rc = SQLITE_OK;
     }else{
+      int nSave = db->busyHandler.nBusy;
       rc = sqlite3OsFileControl(fd, op, pArg);
+      db->busyHandler.nBusy = nSave;
     }
     sqlite3BtreeLeave(pBtree);
   }

src/os_unix.c

@@ -2145,6 +2145,7 @@ static int unixClose(sqlite3_file *id){
   }
   sqlite3_mutex_leave(pInode->pLockMutex);
   releaseInodeInfo(pFile);
+  assert( pFile->pShm==0 );
   rc = closeUnixFile(id);
   unixLeaveMutex();
   return rc;

src/prepare.c

@@ -746,6 +746,7 @@ static int sqlite3LockAndPrepare(
   sqlite3BtreeLeaveAll(db);
   rc = sqlite3ApiExit(db, rc);
   assert( (rc&db->errMask)==rc );
+  db->busyHandler.nBusy = 0;
   sqlite3_mutex_leave(db->mutex);
   return rc;
 }