gtk.cfg: the g_ascii_formatd() value must be initialized

Review of the previous commit: the variadic argument lacked the
<not-uninit/> that gnu.cfg gives its variadic arguments, so an
uninitialized struct member passed as the value was only reported as
uninitvar, without uninitStructMember.

Author: pduchi

cfg/gtk.cfg

@@ -3300,6 +3300,7 @@
     </arg>
     <arg nr="variadic" direction="in">
       <not-bool/>
+      <not-uninit/>
     </arg>
   </function>
   <!-- gboolean g_ascii_isalnum(gchar c); -->

test/cfg/gtk.c

@@ -679,4 +679,11 @@ void g_ascii_formatd_format_test(const gchar *format, int i)
     // cppcheck-suppress invalidFunctionArgBool
     g_ascii_formatd(buf, sizeof(buf), format, i == 1);
     g_print("%s", buf);
+
+    struct {
+        double x;
+    } s;
+    // cppcheck-suppress [uninitvar, uninitStructMember]
+    g_ascii_formatd(buf, sizeof(buf), format, s.x);
+    g_print("%s", buf);
 }