Installd: deleteOdex's outputPath can be null

Add @nullable, as the outputPath can be null for system apps.

Bug: 62236497
Test: m
Test: Fill up /data, apply OTA
Change-Id: I61d86721b485f85195b153d76ce25412dcb68be6
diff --git a/cmds/installd/InstalldNativeService.cpp b/cmds/installd/InstalldNativeService.cpp
index dec23d3..3041467 100644
--- a/cmds/installd/InstalldNativeService.cpp
+++ b/cmds/installd/InstalldNativeService.cpp
@@ -2249,13 +2249,13 @@
 }
 
 binder::Status InstalldNativeService::deleteOdex(const std::string& apkPath,
-        const std::string& instructionSet, const std::string& outputPath) {
+        const std::string& instructionSet, const std::unique_ptr<std::string>& outputPath) {
     ENFORCE_UID(AID_SYSTEM);
     std::lock_guard<std::recursive_mutex> lock(mLock);
 
     const char* apk_path = apkPath.c_str();
     const char* instruction_set = instructionSet.c_str();
-    const char* oat_dir = outputPath.c_str();
+    const char* oat_dir = outputPath ? outputPath->c_str() : nullptr;
 
     bool res = delete_odex(apk_path, instruction_set, oat_dir);
     return res ? ok() : error();