core/remote/watcher: Do not watch if stopped

  The remote watcher can be stopped while it was waiting for the PouchDB
  lock to be free.
  In this case, we've already passed all checks on the running status of
  the watcher and the `watch()` call will be executed once the lock is
  free which we don't want (this can trigger unwanted requests to the
  remote Cozy when the watcher is stopped by Sync because of an
  unreachable Cozy for example).

  Adding another check right after the lock gate prevents this.

core/remote/watcher/index.js

@@ -169,6 +169,11 @@ class RemoteWatcher {
   async watch() /*: Promise<?RemoteError> */ {
     const release = await this.pouch.lock(this)
     try {
+      if (!this.running) {
+        log.debug('Watcher stopped: skipping remote watch')
+        return
+      }
+
       this.events.emit('buffering-start')
 
       const seq = await this.pouch.getRemoteSeq()

test/support/helpers/remote.js

@@ -51,7 +51,9 @@ class RemoteTestHelpers {
   }
 
   async pullChanges() {
+    this.side.watcher.running = true
     await this.side.watcher.watch()
+    this.side.watcher.running = false
   }
 
   async createDirectory(

test/unit/remote/watcher.js

@@ -390,6 +390,7 @@ describe('RemoteWatcher', function () {
       sinon.spy(this.events, 'emit')
 
       this.pouch.getRemoteSeq.resolves(lastLocalSeq)
+      this.watcher.running = true
       this.watcher.processRemoteChanges.resolves([])
       this.remoteCozy.changes.resolves(changes)
     })
@@ -398,6 +399,7 @@ describe('RemoteWatcher', function () {
       this.events.emit.restore()
       this.remoteCozy.changes.restore()
       this.watcher.processRemoteChanges.restore()
+      this.watcher.running = false
       this.pouch.setRemoteSeq.restore()
       this.pouch.getRemoteSeq.restore()
     })
@@ -543,6 +545,34 @@ describe('RemoteWatcher', function () {
         })
       })
     })
+
+    context('when watcher is not running', () => {
+      beforeEach(function () {
+        this.watcher.running = false
+      })
+
+      afterEach(function () {
+        this.watcher.running = true
+      })
+
+      it('returns without fetching changes', async function () {
+        await this.watcher.watch()
+
+        should(this.remoteCozy.changes).not.have.been.called()
+      })
+
+      it('still tries to get hold of the PouchDB lock', async function () {
+        sinon.spy(this.pouch, 'lock')
+
+        try {
+          await this.watcher.watch()
+
+          should(this.pouch.lock).have.been.calledOnce()
+        } finally {
+          this.pouch.lock.restore()
+        }
+      })
+    })
   })
 
   const validMetadata = (