`showEFloat` inconsistency introduced in base-4.12

While base-4.11 had a showEFloat that behaved like

showEFloat (Just n) | n <= 0 == showEFloat (Just 1)

For non-positive values, base-4.12 introduced an unfortunate inconsistency:

showEFloat (Just n) | n < 0 == showEFloat (Just 1)
-- NB: *not* equivalent to     showEFloat (Just 0)

e.g. now we have

showEFloat (Just 2)    1.0 "" == "1.00e0"
showEFloat (Just 1)    1.0 "" == "1.0e0"
showEFloat (Just 0)    1.0 "" == "1e0"
showEFloat (Just (-1)) 1.0 "" == "1.0e0"
showEFloat (Just (-2)) 1.0 "" == "1.0e0"

iow, negative ns in the precision argument are now treated differently from (Just 0) which is a source of subtle bugs for API consumers which assume showEFloat to have "continuous total" (or rather, saturated subtraction) semantics for the precision argument.