Fix/invalid server settings gql mutation request (#1092)

* Validate setting values on mutation

* Handle invalid negative setting values

* Ensure at least one source is downloading at all times

* Prevent possible IllegalArgumentException

The "serverConfig.maxSourcesInParallel" value could have changed after the if-condition

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/extension/ExtensionsList.kt

@@ -224,7 +224,7 @@ object ExtensionsList {
             this
         }
 
-    private val repoMatchRegex =
+    val repoMatchRegex =
         (
             "https:\\/\\/(?>www\\.|raw\\.)?(github|githubusercontent)\\.com" +
                 "\\/([^\\/]+)\\/([^\\/]+)(?>(?>\\/tree|\\/blob)?\\/([^\\/\\n]*))?(?>\\/([^\\/\\n]*\\.json)?)?"