Make ti-fast agent fallback to kArtTiVersion

It is useful to try and use tifast on userdebug devices with
non-debuggable applications.

Test: adb shell am start-activity -S \
          --attach-agent /data/local/tmp/libtifast.so=log,MethodEntry \
          <some non-debuggable apk>

Change-Id: Ic39d99aae1e986e66ac370e078a3b4540087cbbe