adb_root: Simplify the way we parse enabled state file

On a failed conversion, instead of throwing a C++ exception (and we have
exceptions disabled, so we get abort()ed instead), we just say it's
disabled, which is better than crashing.

Change-Id: Ia3e5432b2591b98f8cb5911b39459260b9ac6ba6
diff --git a/root/adbroot_service.cpp b/root/adbroot_service.cpp
index d622fdd..710a521 100644
--- a/root/adbroot_service.cpp
+++ b/root/adbroot_service.cpp
@@ -46,7 +46,7 @@
 ADBRootService::ADBRootService() : enabled_(false) {
     std::string buf;
     if (ReadFileToString(kStoragePath + kEnabled, &buf)) {
-        enabled_ = std::stoi(Trim(buf));
+        enabled_ = Trim(buf) == "1";
     }
 }