Add unconverted reason for jarjar incompatibility.

Test: m bp2build
Change-Id: I112b84fa53f57b9df2bd1e1616012fe55b48001e
diff --git a/java/plugin.go b/java/plugin.go
index 731dfda..5127298 100644
--- a/java/plugin.go
+++ b/java/plugin.go
@@ -66,7 +66,10 @@
 // ConvertWithBp2build is used to convert android_app to Bazel.
 func (p *Plugin) ConvertWithBp2build(ctx android.TopDownMutatorContext) {
 	pluginName := p.Name()
-	commonAttrs, bp2BuildInfo := p.convertLibraryAttrsBp2Build(ctx)
+	commonAttrs, bp2BuildInfo, supported := p.convertLibraryAttrsBp2Build(ctx)
+	if !supported {
+		return
+	}
 	depLabels := bp2BuildInfo.DepLabels
 
 	deps := depLabels.Deps