media.MediaPlayer: don't check file-existence for URI-s with scheme
media.MediaPlayer: don't check file-existence for URI-s with scheme

setDataSource can be called with URI-s as well as with file paths.
Check file-existence only for file:// URI-s as well as URI-s
without scheme (which are assumed to be paths).

Bug: 17109022
Change-Id: I70f16a4f614dcef0b47fa264cf708473036cef4e

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base