Suppress dnsjava warning because of missing Context (#959)

Author: rfc2822

app/src/main/kotlin/at/bitfire/davdroid/network/DnsRecordResolver.kt

@@ -13,6 +13,7 @@ import org.xbill.DNS.ExtendedResolver
 import org.xbill.DNS.Lookup
 import org.xbill.DNS.Record
 import org.xbill.DNS.Resolver
+import org.xbill.DNS.ResolverConfig
 import org.xbill.DNS.SRVRecord
 import org.xbill.DNS.SimpleResolver
 import org.xbill.DNS.TXTRecord
@@ -40,6 +41,11 @@ class DnsRecordResolver @Inject constructor(
 
     private val resolver by lazy { chooseResolver() }
 
+    init {
+        // empty initialization for dnsjava because we set the servers for each request
+        ResolverConfig.setConfigProviders(listOf())
+    }
+
     /**
      * Creates a matching Resolver, depending on the Android version:
      *