Summary:
When the GIF data is not a string nor NSData, `imageSource` is some unknown value set to whatever memory was on the stack. Calling `CGImageSourceGetType` on it has undefined behavior, and if it makes through to the CFRelease (maybe because it is NULL) then CFRelease will crash. This fixes a clang warning.
Closes https://github.com/facebook/react-native/pull/77
Github Author: James Ide <ide@jameside.com>
Test Plan: Imported from GitHub, without a `Test Plan:` line.