libsnapuserd: Handle empty response from server

If server disconnects, then handle the empty response.

Bug: 377068272
Test: Full OTA
Change-Id: Ic48204c457ef924ba9a3c1ae84a3317fb1ccda04
Signed-off-by: Akilesh Kailash <akailash@google.com>

fs_mgr/libsnapshot/snapuserd/snapuserd_client.cpp

@@ -311,6 +311,11 @@ double SnapuserdClient::GetMergePercent() {
     }
     std::string response = Receivemsg();
 
+    // If server socket disconnects most likely because of device reboot,
+    // then we just return 0.
+    if (response.empty()) {
+        return 0.0;
+    }
     return std::stod(response);
 }