Don't emit superfluous LOCAL_OVERRIDES_MODULES

Don't emit an empty LOCAL_OVERRIDES_MODULES line if APEX is not
overriding any module.

Test: TH noop
Change-Id: I7abbaccd54bf2ffa25a6c798260c81284ea5ecb2
diff --git a/apex/androidmk.go b/apex/androidmk.go
index 774b62d..91a405c 100644
--- a/apex/androidmk.go
+++ b/apex/androidmk.go
@@ -233,8 +233,9 @@
 					for _, o := range a.overridableProperties.Overrides {
 						patterns = append(patterns, "%."+o+a.suffix)
 					}
-					fmt.Fprintln(w, "LOCAL_OVERRIDES_MODULES :=", strings.Join(patterns, " "))
-
+					if len(patterns) > 0 {
+						fmt.Fprintln(w, "LOCAL_OVERRIDES_MODULES :=", strings.Join(patterns, " "))
+					}
 					if len(a.compatSymlinks) > 0 {
 						// For flattened apexes, compat symlinks are attached to apex_manifest.json which is guaranteed for every apex
 						postInstallCommands = append(postInstallCommands, a.compatSymlinks...)
@@ -307,7 +308,9 @@
 				fmt.Fprintln(w, "LOCAL_MODULE_PATH :=", a.installDir.ToMakePath().String())
 				fmt.Fprintln(w, "LOCAL_MODULE_STEM :=", name+apexType.suffix())
 				fmt.Fprintln(w, "LOCAL_UNINSTALLABLE_MODULE :=", !a.installable())
-				fmt.Fprintln(w, "LOCAL_OVERRIDES_MODULES :=", strings.Join(a.overridableProperties.Overrides, " "))
+				if len(a.overridableProperties.Overrides) > 0 {
+					fmt.Fprintln(w, "LOCAL_OVERRIDES_MODULES :=", strings.Join(a.overridableProperties.Overrides, " "))
+				}
 				if len(moduleNames) > 0 {
 					fmt.Fprintln(w, "LOCAL_REQUIRED_MODULES +=", strings.Join(moduleNames, " "))
 				}