Fix crash caused by missing shader function definition and report the error. BUG=17956386 Change-Id: I89f243b557b70401052b1f7db237fbc410386f64 Reviewed-on: https://swiftshader-review.googlesource.com/1190 Reviewed-by: Alexis Hétu <sugoi@google.com> Tested-by: <nicolascapens@google.com> Reviewed-by: <nicolascapens@google.com>