snprintf/g_snprintf: do not allow uninitialized target buffer

cfg/gtk.cfg

@@ -2438,8 +2438,23 @@
     <noreturn>false</noreturn>
   </function>
   <function name="g_snprintf">
-    <leak-ignore/>
+    <returnValue type="int"/>
     <noreturn>false</noreturn>
+    <leak-ignore/>
+    <arg nr="1">
+      <not-uninit/>
+      <minsize type="argvalue" arg="2"/>
+    </arg>
+    <arg nr="2">
+      <not-uninit/>
+      <valid>0:</valid>
+    </arg>
+    <formatstr/>
+    <arg nr="3">
+      <formatstr/>
+      <not-null/>
+      <not-uninit/>
+    </arg>
   </function>
   <function name="g_source_remove">
     <leak-ignore/>

cfg/std.cfg

@@ -5813,6 +5813,7 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1">
+      <not-uninit/>
       <minsize type="argvalue" arg="2"/>
     </arg>
     <arg nr="2">

test/cfg/std.c

@@ -3527,7 +3527,7 @@ void uninitvar_snprintf(char *S, size_t N, char *Format, int Int)
     (void)snprintf(S,N,format,Int); // format is uninitialized
     // cppcheck-suppress uninitvar
     (void)snprintf(S,N,Format,i); // i is uninitialized
-    // TODO cppcheck-suppress uninitvar
+    // cppcheck-suppress uninitvar
     (void)snprintf(s,N,Format,Int);
 
     // no warning is expected for