fix getCheckpoint 404 handling on iinitial replication

Author: emilygilberts

packages/node_modules/pouchdb-checkpointer/src/index.js

@@ -193,6 +193,10 @@ class CheckpointerInternal {
           return LOWEST_SEQ;
         }
       }
+      //missing sourceDoc on initial replication returns LOWEST_SEQ
+      if (err.status === 404) {
+        return LOWEST_SEQ;
+      }
       throw err;
     }
   }