Check if NzbGet KeepHistory value is set too high instead of only checking for 0.

src/NzbDrone.Core.Test/Download/DownloadClientTests/NzbgetTests/NzbgetFixture.cs

@@ -414,5 +414,20 @@ namespace NzbDrone.Core.Test.Download.DownloadClientTests.NzbgetTests
 
             error.IsValid.Should().Be(expected);
         }
+
+        [TestCase("0", false)]
+        [TestCase("1", true)]
+        [TestCase(" 7", false)]
+        [TestCase("5000000", false)]
+        public void should_test_keephistory(string keephistory, bool expected)
+        {
+            Mocker.GetMock<INzbgetProxy>()
+                .Setup(v => v.GetConfig(It.IsAny<NzbgetSettings>()))
+                .Returns(new Dictionary<string, string> { { "KeepHistory", keephistory } });
+
+            var error = Subject.Test();
+
+            error.IsValid.Should().Be(expected);
+        }
     }
 }

src/NzbDrone.Core/Download/Clients/Nzbget/Nzbget.cs

@@ -297,7 +297,8 @@ namespace NzbDrone.Core.Download.Clients.Nzbget
             var config = _proxy.GetConfig(Settings);
 
             var keepHistory = config.GetValueOrDefault("KeepHistory");
-            if (keepHistory == "0")
+            int value;
+            if (int.TryParse(keepHistory, out value) || value == 0)
             {
                 return new NzbDroneValidationFailure(string.Empty, "NzbGet setting KeepHistory should be greater than 0")
                 {
@@ -305,6 +306,14 @@ namespace NzbDrone.Core.Download.Clients.Nzbget
                     DetailedDescription = "NzbGet setting KeepHistory is set to 0. Which prevents Sonarr from seeing completed downloads."
                 };
             }
+            else if (value > 25000)
+            {
+                return new NzbDroneValidationFailure(string.Empty, "NzbGet setting KeepHistory should be less than 25000")
+                {
+                    InfoLink = string.Format("http://{0}:{1}/", Settings.Host, Settings.Port),
+                    DetailedDescription = "NzbGet setting KeepHistory is set too high."
+                };
+            }
 
             return null;
         }