fix lib loading regression on iOS

Author: vaind

objectbox/lib/src/native/bindings/bindings.dart

@@ -22,10 +22,11 @@ ObjectBoxC? _tryObjectBoxLibProcess() {
     _lib = DynamicLibrary.process();
     obxc = ObjectBoxC(_lib!);
     _isSupportedVersion(obxc); // may throw in case symbols are not found
+    return obxc;
   } catch (_) {
     // ignore errors (i.e. symbol not found)
+    return null;
   }
-  return null;
 }
 
 ObjectBoxC? _tryObjectBoxLibFile() {

objectbox/lib/src/native/box.dart

@@ -419,16 +419,20 @@ class _AsyncBoxHelper {
     }
 
     port.listen((dynamic message) {
-      // Null is sent if the put was successful (there is no error, thus NULL)
-      if (message == null) {
-        completer.complete(newId);
-      } else if (message is String) {
-        completer.completeError(message.startsWith('Unique constraint')
-            ? UniqueViolationException(message)
-            : ObjectBoxException(message));
-      } else {
-        completer.completeError(ObjectBoxException(
-            'Unknown message type (${message.runtimeType}: $message'));
+      if (!completer.isCompleted) {
+        // Null is sent if the put was successful (there is no error, thus NULL)
+        if (message == null) {
+          completer.complete(newId);
+        } else if (message is String) {
+          print('Received string error message: $message');
+          completer.completeError(message.startsWith('Unique constraint')
+              ? UniqueViolationException(message)
+              : ObjectBoxException(message));
+        } else {
+          print('Received other error message: $message');
+          completer.completeError(ObjectBoxException(
+              'Unknown message type (${message.runtimeType}: $message'));
+        }
       }
       port.close();
     });