[gtk] gtk-demo/main: Suppress implicit fallthru warning

[Daniel Boles <dboles src gnome org>]

commit 9cbd3ac017a993889c5c663603db7867e0d4ed13
Author: Daniel Boles <dboles src gmail com>
Date:   Fri Oct 12 22:09:42 2018 +0100

    gtk-demo/main: Suppress implicit fallthru warning
    
    Comments matched to reassure the compiler that fallthrough is
    intentional are supposed to precede the case or default keywords, at
    least in GCC, so the one here did not suppress the warning with GCC. We
    can just the if condition and put the comment at the end to solve that.
    
    https://developers.redhat.com/blog/2017/03/10/wimplicit-fallthrough-in-gcc-7/

 demos/gtk-demo/main.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)
---
diff --git a/demos/gtk-demo/main.c b/demos/gtk-demo/main.c
index 98f730ae74..ba2f1a25c1 100644
--- a/demos/gtk-demo/main.c
+++ b/demos/gtk-demo/main.c
@@ -831,15 +831,14 @@ load_file (const gchar *demoname,
           /* Skipping blank lines */
           while (g_ascii_isspace (*p))
             p++;
-          if (*p)
-            {
-              p = lines[i];
-              state++;
-              /* Fall through */
-            }
-          else
+
+          if (!*p)
             break;
 
+          p = lines[i];
+          state++;
+          /* Fall through */
+
         case 3:
           /* Reading program body */
           gtk_text_buffer_insert (source_buffer, &start, p, -1);