TpSimplePasswordManager: copy the string into the result
TpSimplePasswordManager: copy the string into the result

Otherwise, if a caller kept a ref to the GAsyncResult after control had
returned to the channel, the channel could have freed the GString
already.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=45554
Signed-off-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>
Reviewed-by: Jonny Lamb <3d1fb3642aaab2ff70e3392a5ab916bf99eed6a3@collabora.co.uk>

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib