Set output for build_prop even on Soong only build

Without this change, Soong only build may break unexpectedly if some
modules refer to the build_prop module.

Bug: 322090587
Test: soong only build
Change-Id: I7571bdf0aa6c08ade8f130842c84c02bb0233acb
diff --git a/android/build_prop.go b/android/build_prop.go
index 45c17c3..ed3e9c8 100644
--- a/android/build_prop.go
+++ b/android/build_prop.go
@@ -60,6 +60,7 @@
 	p.outputFilePath = PathForModuleOut(ctx, "build.prop").OutputPath
 	if !ctx.Config().KatiEnabled() {
 		WriteFileRule(ctx, p.outputFilePath, "# no build.prop if kati is disabled")
+		ctx.SetOutputFiles(Paths{p.outputFilePath}, "")
 		return
 	}