Always set apex_available in SDK snapshots.

Also fix //apex_available:platform that could get lost in the generated
apex_available properties. It only happened if a module didn't specify
an apex_available setting and then got extra entries from
apex.BaselineApexAvailable.

Test: Build ART SDK with libnativeloader_lazy in the SDK, and check
  that the generated prebuilt module has //apex_available:platform
  (before https://r.android.com/1480559).
Change-Id: I9df20aee63455932a7e558993f0f26769cb02792
diff --git a/sdk/update.go b/sdk/update.go
index 7bf5dea..ba63542 100644
--- a/sdk/update.go
+++ b/sdk/update.go
@@ -735,6 +735,24 @@
 		}
 	}
 
+	// Where available copy apex_available properties from the member.
+	if apexAware, ok := variant.(interface{ ApexAvailable() []string }); ok {
+		apexAvailable := apexAware.ApexAvailable()
+		if len(apexAvailable) == 0 {
+			// //apex_available:platform is the default.
+			apexAvailable = []string{android.AvailableToPlatform}
+		}
+
+		// Add in any baseline apex available settings.
+		apexAvailable = append(apexAvailable, apex.BaselineApexAvailable(member.Name())...)
+
+		// Remove duplicates and sort.
+		apexAvailable = android.FirstUniqueStrings(apexAvailable)
+		sort.Strings(apexAvailable)
+
+		m.AddProperty("apex_available", apexAvailable)
+	}
+
 	deviceSupported := false
 	hostSupported := false
 
@@ -749,22 +767,6 @@
 
 	addHostDeviceSupportedProperties(deviceSupported, hostSupported, m)
 
-	// Where available copy apex_available properties from the member.
-	if apexAware, ok := variant.(interface{ ApexAvailable() []string }); ok {
-		apexAvailable := apexAware.ApexAvailable()
-
-		// Add in any baseline apex available settings.
-		apexAvailable = append(apexAvailable, apex.BaselineApexAvailable(member.Name())...)
-
-		if len(apexAvailable) > 0 {
-			// Remove duplicates and sort.
-			apexAvailable = android.FirstUniqueStrings(apexAvailable)
-			sort.Strings(apexAvailable)
-
-			m.AddProperty("apex_available", apexAvailable)
-		}
-	}
-
 	// Disable installation in the versioned module of those modules that are ever installable.
 	if installable, ok := variant.(interface{ EverInstallable() bool }); ok {
 		if installable.EverInstallable() {