Add explicit Result::ok() checks where needed

Test: m checkbuild continuous_instrumentation_tests continuous_instrumentation_tests_api_coverage continuous_native_tests device-tests platform_tests
Exempt-From-Owner-Approval: mechanical mass refactoring
Change-Id: I3117833c51cdb333cccdfd159d1582f2adef77db
diff --git a/tools/aapt2/util/Util.cpp b/tools/aapt2/util/Util.cpp
index ef33c34..793a236 100644
--- a/tools/aapt2/util/Util.cpp
+++ b/tools/aapt2/util/Util.cpp
@@ -531,14 +531,14 @@
 }
 
 StringPiece16 GetString16(const android::ResStringPool& pool, size_t idx) {
-  if (auto str = pool.stringAt(idx)) {
+  if (auto str = pool.stringAt(idx); str.ok()) {
     return *str;
   }
   return StringPiece16();
 }
 
 std::string GetString(const android::ResStringPool& pool, size_t idx) {
-  if (auto str = pool.string8At(idx)) {
+  if (auto str = pool.string8At(idx); str.ok()) {
     return ModifiedUtf8ToUtf8(str->to_string());
   }
   return Utf16ToUtf8(GetString16(pool, idx));