Fix pattern match on buildLoaders.

Fixes #1341

main/src/main/scala/sbt/Load.scala

@@ -270,7 +270,7 @@ object Load
 		loaders updatePluginManagement PluginManagement.extractOverrides(unit.plugins.fullClasspath)
 
 	def addResolvers(unit: sbt.BuildUnit, isRoot: Boolean, loaders: BuildLoader): BuildLoader =
-		unit.definitions.builds.flatMap(_.buildLoaders) match
+		unit.definitions.builds.flatMap(_.buildLoaders).toList match
 		{
 			case Nil => loaders
 			case x :: xs =>

sbt/src/sbt-test/project/build-loaders/project/build.scala

@@ -0,0 +1,12 @@
+import sbt._
+import Keys._
+
+object EmptyLoaderBuild extends Build {
+  override def buildLoaders = BuildLoader.transform(_.unit) :: Nil
+  lazy val root = (
+    project in file(".")
+    settings(
+      name := "foo"
+    )
+  )
+}

sbt/src/sbt-test/project/build-loaders/test

@@ -0,0 +1,2 @@
+# Just making sure the build compiles is enough of a test.
+> name