correctly reset path for rules without specific command

This is a fixup for commit 01c658f
where the behaviour was changed to not inherit the PATH variable
by default.

doas.c

@@ -386,6 +386,7 @@ main(int argc, char **argv)
 
 #ifdef HAVE_LOGIN_CAP_H
 	if (setusercontext(NULL, targpw, target, LOGIN_SETGROUP |
+	    LOGIN_SETPATH |
 	    LOGIN_SETPRIORITY | LOGIN_SETRESOURCES | LOGIN_SETUMASK |
 	    LOGIN_SETUSER) != 0)
 		errx(1, "failed to set user context for target");
@@ -396,6 +397,8 @@ main(int argc, char **argv)
 		err(1, "initgroups");
 	if (setresuid(target, target, target) != 0)
 		err(1, "setresuid");
+	if (setenv("PATH", safepath, 1) == -1)
+		err(1, "failed to set PATH '%s'", safepath);
 #endif
 
 	if (getcwd(cwdpath, sizeof(cwdpath)) == NULL)