Richard Eisenberg authored Jan 17, 2019 and Marge Bot committed Feb 12, 2019

There was an awful lot of zipping going on in
canDecomposableTyConAppOK, and one of the lists being zipped
was too short, causing the result to be too short. Easily
fixed.

Also fixes #16204 and #16225

test case: typecheck/should_compile/T16188
           typecheck/should_compile/T16204[ab]
           typecheck/should_fail/T16204c
           typecheck/should_compile/T16225