dumpstate: Skip subsequent showmaps if the first run fails.

dumpstate takes over six minutes to run as each call to "su" (which
dumpstate uses opportunistically on states that require root privileges to
access) takes approximately one second to process.

The vast majority of these "su" calls are made to "showmap", which is
called for every running process.  These calls nearly always fail, either
because dumpstate is denied root access, or because "showmap" isn't
installed.

This greatly speeds up the dumpstate process by skipping subsequent
"showmap" attempts if the first run (on process init) fails.