Fix issue with INIT_WITH of array/list/....

combined with tuple:
_push_back_raw was used within an expanded macro
and as a consequence was expanded multiple times,
resulting in adding a new term in the sequence
for each field of the tuple.

m-core.h

@@ -3655,9 +3655,14 @@ m_core_parse2_enum (const char str[], const char **endptr)
 #define M_INIT_WITH_VAI22_FUNC(pair, a)                                       \
   M_INIT_WITH_VAI23_FUNC(M_PAIR_1 pair, M_PAIR_2 pair, a)
 
+/* We first push a raw new item, and then we get back its pointer using _back.
+  _back (contrary to _push_raw) has no side effect, and so is safe to be used
+  in a macro */  
 #define M_INIT_WITH_VAI23_FUNC(d, op, a)                                      \
-  M_IF(M_PARENTHESIS_P( a ))(M_CALL_INIT_WITH, M_CALL_INIT_SET)(M_GET_OPLIST op, *M_C( M_GET_NAME op , _push_raw)(d), M_REMOVE_PARENTHESIS (a))
-
+  (                                                                           \
+    (void) M_C(M_GET_NAME op, _push_raw)(d),                                  \
+    M_IF(M_PARENTHESIS_P( a ))(M_CALL_INIT_WITH, M_CALL_INIT_SET)(M_GET_OPLIST op, *M_C( M_GET_NAME op , _back)(d), M_REMOVE_PARENTHESIS (a)) \
+  )
 
 /* Initialize the container 'dest' as per 'oplist' INIT operator
    and fill it with the given VA argument