Fix .equals call in ImageDecoder

Bug: 154954875
Bug: 143231863
Test: I93b01cb60a8c76110ea2ff4250d0048512629d8d

I9229039b752bafa9a9b85b914a62093dff1eec34 switched from "==" to
".equals", but it did not take into account that Uri#getScheme() can
return null. Switch around the .equals check so that it is called on
SCHEME_CONTENT, which will never be null.

Change-Id: I0df5d2407a32fad0e21e597697af293fbc2fb315
Merged-In: I0df5d2407a32fad0e21e597697af293fbc2fb315