Add check that both comparison keys are not blank

We want to know if this happens as soon as possible, as it will almost
always result in operations being combined when they should not.

Author: jkasten2

OneSignalSDK/onesignal/core/src/main/java/com/onesignal/core/internal/operations/impl/OperationRepo.kt

@@ -278,6 +278,10 @@ internal class OperationRepo(
                 val itemKey =
                     if (startingOp.operation.groupComparisonType == GroupComparisonType.CREATE) item.operation.createComparisonKey else item.operation.modifyComparisonKey
 
+                if (itemKey == "" && startingKey == "") {
+                    throw Exception("Both comparison keys can not be blank!")
+                }
+
                 if (itemKey == startingKey) {
                     queue.remove(item)
                     ops.add(item)