Update SHA1PRNG_SecureRandomImpl to patch fix for CVE-2013-7372

Patch for vulnerability in SHA1PRNG_SecureRandomImpl caused when no seed if provided by the user.
More information available: http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-7372. 
The fix originated in this commit to the Android libcore: https://android.googlesource.com/platform/libcore/+/ab6d7714b47c04cc4bd812b32e6a6370181a06e4%5E%21/#F0