* src/transform.c (xfm_lens): initialize *lens_name to NULL
* src/transform.c (xfm_lens): initialize *lens_name to NULL

Otherwise, we might deal with an uninitialized lens_name in callers,
something that gcc 7.1 spots under -O3.

kunkku/augeas,lutter/augeas,kunkku/augeas,hercules-team/augeas,mlichvar/augeas,kunkku/augeas,mlichvar/augeas,pevalme/augeas,ptoscano/augeas,lutter/augeas,mlichvar/augeas,hercules-team/augeas,pevalme/augeas,pevalme/augeas,ptoscano/augeas,ptoscano/augeas,lutter/augeas