sh_binary: Use pointers for optional attributes

Empty strings for filename and sub_dir were unnecessicarily always being
propagated to BUILD files.

Test: build/bazel/ci/bp2build.sh
Change-Id: I39d6af12b1decd1d3813b92daa862ebc025daa7d

sh/sh_binary.go

@@ -511,8 +511,8 @@ func ShTestHostFactory() android.Module {
 
 type bazelShBinaryAttributes struct {
 	Srcs     bazel.LabelListAttribute
-	Filename string
-	Sub_dir  string
+	Filename *string
+	Sub_dir  *string
 	// Bazel also supports the attributes below, but (so far) these are not required for Bionic
 	// deps
 	// data
@@ -538,14 +538,14 @@ func (m *ShBinary) ConvertWithBp2build(ctx android.TopDownMutatorContext) {
 	srcs := bazel.MakeLabelListAttribute(
 		android.BazelLabelForModuleSrc(ctx, []string{*m.properties.Src}))
 
-	var filename string
+	var filename *string
 	if m.properties.Filename != nil {
-		filename = *m.properties.Filename
+		filename = m.properties.Filename
 	}
 
-	var subDir string
+	var subDir *string
 	if m.properties.Sub_dir != nil {
-		subDir = *m.properties.Sub_dir
+		subDir = m.properties.Sub_dir
 	}
 
 	attrs := &bazelShBinaryAttributes{