exec/2,3 spawn process even when error raised (0925)

exec/2,3 raises error 192 (illegal stream mode) as expected if the stream
list (2nd arg) has problems:

[eclipse 1]: exec(hello, [output,input,error]).
illegal stream mode in exec(hello, [output, input, error], _211)
[eclipse 2]: exec(hello, [output,input,error], P).
illegal stream mode in exec(hello, [output, input, error], P)

However, it still spawn the process that then perform the exec:


[eclipse 4]: 1.
exec(hello, [output, input, error]).
illegal stream mode in exec(hello, [output, input, error], _275)
[eclipse 5]: wait(X,Y).

X = 11616
Y = 33280     More? (;) 


no (more) solution.
[eclipse 6]: 2.
exec(hello, [output, input, error], P).
illegal stream mode in exec(hello, [output, input, error], P)
[eclipse 7]: wait(X,Y).

X = 11617
Y = 33280     More? (;) 

no (more) solution.
[eclipse 8]: 

This seems wrong, as I would expect that no process will be spawned to
perform the exec when there is an error, in particular for exec/2, which is
supposed to wait for the process to return, instead of spawning a process
and return.