firstboot/homectl: hide plymouth splashscreen when asking questions

When plymouth is enabled, the screen gets all garbled when firstboot
runs and asks questions. Disable the splash screen, but only when
actually asking questions.

src/firstboot/firstboot.c

@@ -43,6 +43,7 @@
 #include "parse-util.h"
 #include "password-quality-util.h"
 #include "path-util.h"
+#include "plymouth-util.h"
 #include "pretty-print.h"
 #include "proc-cmdline.h"
 #include "prompt-util.h"
@@ -110,6 +111,10 @@ static void print_welcome(int rfd, sd_varlink **mute_console_link) {
         assert(rfd >= 0);
         assert(mute_console_link);
 
+        /* Needs to be called before mute_console or it will garble the screen */
+        if (arg_welcome)
+                (void) plymouth_hide_splash();
+
         if (!*mute_console_link && arg_mute_console)
                 (void) mute_console(mute_console_link);